Metals in Motion: Understanding Labile Metal Pools in Bacteria

May combine two claims.

Zn2+ and Cu+ have a high affinity for ligands, with small labile pools and no free, fully hydrated ions at equilibrium.

“Zn2+ and Cu+ have a high affinity for ligands, with small labile pools and no free, fully hydrated ions at equilibrium.3,12”

• cites [3] sourcePartly supported

  The Mismetalation section says Cu+ forms exceptionally tight complexes, and the Associative metalation and available metal section describes extensive Zn2+ binding and a negligible source of unbound Zn2+. The paper does not establish that both metals have small labile pools or that neither has any fully hydrated ions at equilibrium; it discusses an extremely low, rather than strictly zero, availability of hydrated Zn2+. (LLM, conf=0.82)

  Experimental — accuracy not yet measured
• cites [12] sourceNot checked — no full text of the source

• AssumptionRests on an assumption: Features of labile metal pools found in model systems such as Escherichia coli and Bacillus subtilis are broadly conserved across bacteria.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

K+ maintains osmotic balance and is an important contributor to the membrane potential.

“This dominant cation maintains osmotic balance7,46,47 and is an important contributor to the membrane potential.48”

• cites [7] sourceSupported
• cites [46] sourceSupported
• cites [47] sourceNot checked — no full text of the source
• cites [48] sourceSupported

May combine two claims.

For Zn2+ and Cu+, the notional free metal pool is less than one atom per cell at equilibrium, and metal mobility relies on ligand exchange chemistry.

“For Zn2+ and Cu+, however, the notional free metal pool is less than one atom per cell at equilibrium, and the mobility of metals relies on ligand exchange chemistry.3,31,32”

• cites [3] sourcePartly supported

  In “Associative metalation and available metal” (page unavailable), the paper says that femtomolar Zn2+ availability corresponds to far less than one atom per E. coli cell volume, and it describes Cu+ transfer by ligand exchange. It does not give a corresponding per-cell calculation for free Cu+, and it presents ligand exchange as a route for metalation rather than establishing that all metal mobility relies on it. (LLM, conf=0.84)

  Experimental — accuracy not yet measured
• cites [31] sourcePartly supported

  The Introduction (page unavailable) says Cu and Zn are buffered at low available concentrations and that metals move between binding sites through associative exchange reactions. It does not state that the notional free Zn²⁺ or Cu⁺ pool is less than one atom per cell at equilibrium. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [32] sourcePartly supported

  The Conclusions (page unavailable) say that ligand-exchange kinetics enable zinc redistribution, and the zinc-speciation section says zinc transport involves multiple ligand exchanges. The paper does not establish a free pool of less than one atom per cell at equilibrium or extend these statements to Cu+; its discussion of the cellular free pool instead estimates zinc concentrations at a few hundred picomolar. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

At equilibrium, free metal pools are significant for K+ and Mg2+ and are composed of both free and weakly complexed ions.

“At equilibrium, free metal pools are significant for K+ and Mg2+ and are composed of both free and weakly complexed ions.5−7”

• cites [5] sourcePartly supported

  The main text (section headed “Knud H. Nierhaus”; page not provided) reports free Mg2+ at 2–5 mM and intracellular K+ at 60–150 mM under stress-free conditions. It does not say that both have significant free pools at equilibrium or that those pools include weakly complexed ions. (LLM, conf=0.84)

  Experimental — accuracy not yet measured
• cites [6] sourceNot checked — no full text of the source
• cites [7] sourcePartly supported

  The Introduction section on K+ transport and equilibrium ion distributions (page unavailable) describes substantial intracellular K+ concentrations and how K+ distributes across the membrane at equilibrium. It does not establish a significant free Mg2+ pool or say that either pool comprises both free and weakly complexed ions. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

May combine two claims.

The bulk ions (K+, Mg2+) have a low affinity for ligands and a large labile pool.

“The bulk ions (K+, Mg2+) have a low affinity for ligands and a large labile pool,5,6”

• cites [5] sourcePartly supported

  In the Nierhaus commentary (page not provided), Mg²⁺ and K⁺ are described as prevalent intracellular ions, and bound and free Mg²⁺ are said to be in equilibrium. But the paper does not establish low affinity for ligands or a large labile pool for both ions; it reports only 1–5 mM free Mg²⁺ out of about 100 mM total. (LLM, conf=0.84)

  Experimental — accuracy not yet measured
• cites [6] sourceNot checked — no full text of the source

• AssumptionRests on an assumption: Features of labile metal pools found in model systems such as Escherichia coli and Bacillus subtilis are broadly conserved across bacteria.

Probably not a substantial claim: may not pass S3 (load-bearing).

The brackets in Figure 2 denote the range of free metal concentrations corresponding to a 10-90% change in gene expression for the indicated metalloregulators purified from Salmonella and the MgtE riboswitch from B. subtilis.

“The brackets denote the range of free metal concentrations corresponding to a 10–90% change in gene expression as calculated for the indicated metalloregulators purified from Salmonella(4) and the MgtE riboswitch from B. subtilis.29”

• cites [4] sourcePartly supported

  The Results section (‘Low buffered cytosolic metal relative to metal cell−1’; page unavailable) calculates Salmonella metalloregulator responses across buffered metal concentrations. The Online Methods (‘Mathematical calculations’; page unavailable) specifies that these responses are normalized DNA-promoter occupancy, not a 10–90% change in gene expression; our copy does not give that range. The MgtE riboswitch is attached to a separate citation (29), so it is not judged against this source. (LLM, conf=0.83)

  Experimental — accuracy not yet measured
• cites [29] sourceNot checked — no full text of the source

May combine two claims.

Manganese and iron have variable quotas of up to 1 mM, with iron > manganese in most bacteria.

“The moderate affinity ions, manganese (purple) and iron (red), have variable quotas of up to 1 mM, with iron > manganese in most bacteria.11”

• cites [11] sourcePartly supported

  The Introduction says most bacteria have a low manganese requirement and generally use iron rather than manganese as an enzyme cofactor, supporting the broad comparison. It does not establish quotas of up to 1 mM for either metal; the section on manganese-centric bacteria instead reports 30–35 mM intracellular manganese in L. plantarum. Page numbers were not available in our copy. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

The tendency for metal ions in aqueous solution to interact tightly with ligands is summarized in the Irving-Williams series: Mg2+ < Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ (and Cu+) > Zn2+.

“The tendency for metal ions in aqueous solution to interact tightly with ligands is summarized in the Irving-Williams series21,22 (here augmented with Mg2+ and Cu+): Mg2+ < Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ (and Cu+) > Zn2+.”

• cites [21] sourceNot checked — no full text of the source
• cites [22] sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The complex molecular mixture is animated by both thermally driven diffusion and metabolism, which plays a key role in maintaining the cell interior in a fluid state.

“This complex molecular mixture is animated by both thermally driven diffusion and metabolism, which plays a key role in maintaining the cell interior in a fluid state.38”

• cites [38] sourceSupported

May combine two claims.

Zur proteins sense Zn2+ sufficiency and the binding of Zn2+ is anywhere from 10- to 103-fold tighter when measured in the presence of DNA.

“For example, Zur proteins sense Zn2+ sufficiency and the binding of Zn2+ is anywhere from 10- to 103-fold tighter when measured in the presence of DNA.25,27,28”

• cites [25] sourceSupported
• cites [27] sourcePartly supported

  The Results and Discussion section, “Zinc is a Positive Allosteric Effector of AbZur-DNA Binding” (page unavailable), supports that Zur responds to zinc and that zinc binding is tighter in the presence of DNA. But its measured value for Acinetobacter baumannii Zur is approximately 3-fold tighter than for the free protein, not within the claimed 10- to 10³-fold range. (LLM, conf=0.90)

  Experimental — accuracy not yet measured
• cites [28] sourcePartly supported

  In Results, “Thermodynamic data predict the responses to Zn(II),” Zur responds to zinc, supporting its role as a zinc sensor. In Results, “Co(II) affects DNA binding by Zur, FrmRE64H and ZntR,” the paper reports that zinc-bound Salmonella Zur binds DNA about 500-fold more tightly than apo-Zur and calculates coupling between zinc and DNA binding. It does not report measuring zinc-binding affinity in the presence of DNA, or establish the stated 10- to 10³-fold range across Zur proteins; the measured comparison is in the opposite binding direction. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

May combine two claims.

Cells adapt to the stress of osmotic shock through the synthesis or import of compatible solutes and growth resumes after a substantial lag.

“Cells adapt to the stress of osmotic shock through the synthesis or import of compatible solutes and growth resumes after a substantial lag.”

• cites [77] sourceSupported

May combine two claims.

The overall manganese quota varies widely, with the Mn:Fe ratio varying by more than 6 orders of magnitude.

“The overall manganese quota varies widely, with the ratio of Mn:Fe ratio varying by >6 orders of magnitude.97”

• cites [97] sourceSupported

May combine two claims.

The bulk of the quota for manganese and iron is devoted to intracellular enzymes, with a variable fraction partitioned to the membrane or to extracellular enzymes, and the latter may require dedicated maturation pathways.

“The bulk of the quota for manganese and iron is devoted to intracellular enzymes (Figure 3), with a variable fraction partitioned to the membrane (e.g., respiratory complexes) or to extracellular enzymes. The latter may require dedicated pathways for their maturation.95,96”

• cites [95] sourceSupported
• cites [96] sourcePartly supported

  The ‘Metalation of Extracytoplasmic Enzymes’ section describes pathways for maturing exoenzymes, including export after metalation and metal loading outside the cell. The ‘Major Pathways for Metalation of Cytosolic Enzymes’ section says free Mn and Fe are often about 1% of the cellular quota, but does not establish that the bulk is devoted to intracellular enzymes or quantify a variable fraction allocated to membrane and extracellular enzymes. Page numbers are unavailable in our copy. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Manganese is a critical element for most forms of life, although levels of manganese are exceedingly low in some bacteria.

“Manganese (Mn) is a critical element for most forms of life, although levels of manganese are exceedingly low in some bacteria.97”

• cites [97] sourceSupported

May combine two claims.

Ribosomal RNA is the single most abundant RNA in the cell, and both K+ and Mg2+ are essential for ribosome function.

“Ribosomal RNA is the single most abundant RNA in the cell, and both K+ and Mg2+ are essential for ribosome function.53”

• cites [53] sourcePartly supported

  The section “Metal Ions at the PTC in Extant Ribosomes” reports that mammalian ribosomes lose polymerizing activity without potassium and describes magnesium as indispensable for ribosome maintenance, structural integrity, and the PTC reaction. Our copy does not support the separate claim that rRNA is the single most abundant RNA in the cell (searched for cellular rRNA abundance and related terms). (LLM, conf=0.87)

  Experimental — accuracy not yet measured

May combine two claims.

Homologues of Mg2+-dechelatase are present in some nonphotosynthetic Bacteria and Archaea but are lacking in cyanobacteria.

“Although homologues are present in some nonphotosynthetic Bacteria and Archaea,87,88 they are lacking in the cyanobacteria.”

• cites [87] sourceSupported
• cites [88] sourcePartly supported

  The Introduction (page not available in our copy) says SGR homologs occur in nonphotosynthetic bacteria and gives an Anaerolineae bacterium as an example. It does not address their presence in Archaea or their absence from cyanobacteria, so those parts of the claim are unsupported. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

Long-wavelength X-ray crystallography suggested a total of ~600 Mg2+ with 334 having inner-sphere coordination and 251 outer sphere coordination.

“Long-wavelength X-ray crystallography suggested a total of ∼600 Mg2+ with 334 having inner-sphere coordination and 251 outer sphere coordination52 (Figure 4).”

• cites [52] sourcePartly supported

  The Results (Metal ions assignment; page unavailable) report 334 Mg²⁺ ions and 251 modeled as Mg(H₂O)₆²⁺ in the elongation complex, totaling 585—approximately 600. The paper does not classify those two counts as inner- and outer-sphere coordination, and notes that ions modeled as Mg²⁺ may also be hydrated. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

In the ribosome, just over half of ions assigned as Mg2+ retain four or more water molecules as ligands, with the most common RNA-associated inner sphere ligands being nonbridging oxygen atoms from the phosphate backbone.

“In the ribosome, just over half of ions assigned as Mg2+ retain four or more water molecules as ligands, with the most common RNA-associated, inner sphere ligands being the nonbridging oxygen atoms from the phosphate backbone.65”

• cites [65] sourcePartly supported

  The Results section on Mg2+ coordination reports that only around 30% of assigned ribosomal Mg2+ sites have even four or more inner-sphere ligands of any kind, contrary to the claim that just over half have four or more water ligands. The Results section on nucleotide-atom frequencies supports the other part: phosphate oxygen is the most commonly observed RNA inner-sphere ligand. Our copy provides no page numbers for these passages. (LLM, conf=0.90)

  Experimental — accuracy not yet measured

May combine two claims.

Cellular quotas for manganese and iron are variable and typically <1 mM, about 100-fold lower than K+ and Mg2+ (≥100 mM).

“Although both are critical nutrients for most bacteria, the cellular quotas for these metals are variable and typically <1 mM,11 a value ∼100-fold lower than K+ and Mg2+ (≥100 mM).”

• cites [11] sourcePartly supported

  The Introduction says bacterial requirements for manganese and iron differ by species and that most bacteria have a low manganese requirement under normal growth conditions. It does not establish that cellular quotas for both metals are typically below 1 mM; the “Manganese-centric bacteria” section instead gives an example of 30–35 mM intracellular manganese in L. plantarum. The K+ and Mg2+ comparison follows the citation in the citing sentence and is not assessed as attributed to this source. (LLM, conf=0.79)

  Experimental — accuracy not yet measured

May combine two claims.

Both Mg2+ and K+ function in charge neutralization as mobile, outer-sphere ions, with Mg2+ favored at sites of unusually high negative charge density.

“Both Mg2+ and K+ therefore function in charge neutralization as mobile, outer-sphere ions, with Mg2+ favored at sites of unusually high negative charge density.66”

• cites [66] sourcePartly supported

  The Discussion (§§4.1–4.2) describes outer-sphere Mg2+ binding in charge neutralization, and the Conclusions (§4.7) say K+ can neutralize charge while Mg2+ is used at unusually negative pockets. The cited passages do not establish that K+ acts specifically as a mobile, outer-sphere ion. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

In B. subtilis, hyperosmotic shock leads to a large accumulation of intracellular K+ (≥700 mM), which mobilizes Mg2+ ions.

“In B. subtilis, hyperosmotic shock leads to a large accumulation of intracellular K+ (≥700 mM), which mobilizes Mg2+ ions.77”

• cites [77] sourcePartly supported

  The Discussion says osmotic upshift can raise intracellular K+ in B. subtilis to levels approaching 1 M, consistent with ≥700 mM. The Results report that the K+ spike coincides with a sharp drop in cellular Mg2+, but describe K+ displacing Mg2+ as a postulate, not an established causal mechanism. No page numbers were available in our copy. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

May combine two claims.

The thick cell walls of Gram-positive bacteria have an enormous ion-binding capacity, with near equal contributions from peptidoglycan and teichoic acids.

“Similarly, the thick cell walls of Gram-positive bacteria have an enormous ion-binding capacity,61 with near equal contributions from peptidoglycan and teichoic acids.62”

• cites [61] sourceCould not verify

  Citation 62 is attached specifically to the claim of near-equal ion-binding contributions from peptidoglycan and teichoic acids. The Introduction says teichoic acids may constitute up to 60% of the wall’s mass and describes their role in binding cations, but neither that passage nor the passages retrieved for equal contributions and binding capacity compares the two components’ ion-binding contributions. (LLM, conf=0.74)

  Experimental — accuracy not yet measured
• cites [62] sourcePartly supported

  The cell-surface section reports roughly equal contributions from teichoic-acid polyphosphate groups and peptidoglycan carboxyl groups, but specifically for calcium and magnesium binding in Gram-positive cell walls. Citation 62 supports that narrower finding, not an equal contribution to ion binding generally; the separate claim about enormous capacity is attached to citation 61. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

Other estimates of the contribution of the ribosome to Mg2+ pools are in the same range, corresponding to ~12 mM in E. coli or as much as ~25% of the quota.

“Other estimates of the contribution of the ribosome to Mg2+ pools are in this same range, corresponding to ∼12 mM in E. coli(5) or as much as ∼25% of the quota.60”

• cites [5] sourcePartly supported

  In the main text (page unavailable), Nierhaus says E. coli ribosomes bind about 12 mM Mg²⁺ out of about 100 mM total—roughly 12% of the quota. This supports a substantial ribosomal contribution, but not the approximately 25% figure attached to this citation. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [60] sourceSupported

May combine two claims.

E. coli is iron-centric and Mn2+ import is specifically induced as a response to oxidative stress.

“E. coli falls in this category and Mn2+ import is specifically induced as a response to oxidative stress.89,90”

• cites [89] sourceSupported
• cites [90] sourceSupported

May combine two claims.

This Mg2+ can be readily displaced by Fe2+ or Mn2+ leading to enzyme inhibition, suggesting that this Mg2+ is labile.

“This Mg2+ can be readily displaced by Fe2+ or Mn2+ leading to enzyme inhibition,81,82 suggesting that this Mg2+ is labile.”

• cites [81] sourcePartly supported

  The Results report that Fe(II) binds at the catalytic magnesium site and inhibits MST enzymes in the presence of magnesium. The Discussion says magnesium dissociates after each catalytic cycle, consistent with its being labile. The cited passages do not establish displacement or inhibition by Mn(II), or show that Fe(II) directly displaces magnesium already bound to the enzyme. (LLM, conf=0.87)

  Experimental — accuracy not yet measured
• cites [82] sourceSupported

May combine two claims.

>3000 cation-binding sites were visualized in the Thermus thermophilus 70S ribosome and assigned as Mg2+, but those assignments have been challenged on experimental and stereochemical grounds.

“As an upper limit, > 3000 cation-binding sites were visualized in the Thermus thermophilus 70S ribosome51 and assigned as Mg2+, but those assignments have been challenged on both experimental52 and stereochemical54 grounds.”

• cites [51] sourceNot checked — no full text of the source
• cites [52] sourceSupported
• cites [54] sourceSupported

May combine two claims.

In the E. coli 70S ribosome, 309 Mg2+ and 2 Zn2+ ions were assigned by cryo-EM, but K+ was not included in the solvent and was not assigned.

“In the E. coli 70S ribosome, 309 Mg2+ and 2 Zn2+ ions were assigned by this method, but K+ was not included in the solvent and was not assigned.67”

• cites [67] sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

In human physiology, sequestration of iron is a central feature of nutritional immunity, and pathogens have evolved mechanisms to liberate iron from host stores.

“In human physiology, sequestration of iron is a central feature of nutritional immunity,120 and pathogens have evolved a wide variety of mechanisms to liberate iron from host stores.121”

• cites [120] sourceSupported
• cites [121] sourceSupported

May combine two claims.

Some iron-binding enzymes behave more as iron-activated enzymes rather than stable metalloproteins, and Fur is unusually abundant and could also function as an Fe2+-buffering protein.

“Some iron-binding enzymes behave more as iron-activated enzymes rather than stable metalloproteins,148 and Fur is unusually abundant for a regulator and could also function as an Fe2+-buffering protein.101”

• cites [148] sourceSupported
• cites [101] sourcePartly supported

  Citation 101 attaches to the Fur clause, not the preceding claim about iron-binding enzymes. The Abstract says BsFur buffers intracellular Fe(II) at approximately 1 μM, supporting the proposed buffering role. Our copy discusses elevated Fur levels in a perR mutant, but does not establish that Fur is unusually abundant compared with other regulators. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

May combine two claims.

Stored iron pools are in the form of ferric-hydroxide and ferric-hydroxyphosphate complexes and can be monitored using Mössbauer spectroscopy.

“These stored iron pools are in the form of ferric-hydroxide and ferric-hydroxyphosphate complexes and can be monitored using Mössbauer spectroscopy.130,131”

• cites [130] sourcePartly supported

  The Results (page not provided) use Mössbauer spectroscopy to examine cellular iron and identify magnetic ferric cores likely associated with ferritin. Our copy does not identify those stores specifically as ferric-hydroxide or ferric-hydroxyphosphate complexes; searches for hydroxyphosphate and ferric hydroxide did not find that composition. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [131] sourceNot checked — no full text of the source

May combine two claims.

D. radiodurans has a high manganese quota (up to 4 mM) and an exceptionally high Mn/Fe ratio (0.24).

“This bacterium, notable for its exceptionally high resistance to ionizing radiation, has a high manganese quota (up to 4 mM) and an exceptionally high Mn/Fe ratio (0.24).116”

• cites [116] sourceSupported

May combine two claims.

Free Mn2+ in the 3 to 6 μM range represents sufficiency, and levels approaching 10 μM represent excess.

“These analyses suggest that free Mn2+ in the 3 to 6 μM range represents sufficiency (Figure 2), and levels approaching 10 μM represent excess.102”

• cites [102] sourcePartly supported

  The Results section on MntR regulation (page unavailable) supports a distinction between Mn(II) sufficiency and elevated Mn(II): uptake repression begins near 0.5 μM external Mn(II), while efflux expression is half-maximal near 50 μM external Mn(II). It does not identify 3–6 μM free Mn²⁺ as sufficient or levels approaching 10 μM free Mn²⁺ as excess; those numerical thresholds and the claim about free rather than external Mn(II) are unsupported. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

Mobilization of stored iron pools often requires reduction, or in some cases proteolysis, and occurs on a time-scale of minutes.

“Mobilization of these stored iron pools often requires reduction,132 or in some cases proteolysis,127,133 and occurs on a time-scale of minutes.”

• cites [132] sourcePartly supported

  The Introduction (page unavailable) identifies lysosomal ferritin proteolysis as a primary mechanism for mobilizing iron from ferritin, and the Discussion also describes reductive mechanisms. The cited copy does not establish the claim’s minutes-long time scale; its Results discuss release kinetics extending over two hours. (LLM, conf=0.84)

  Experimental — accuracy not yet measured
• cites [127] sourceNot checked — no full text of the source
• cites [133] sourcePartly supported

  The Results report that ClpXP proteolyzes the iron-storage protein Dps, and the Discussion gives a 10-minute half-life for Dps in unstressed cells (pages unavailable). This supports proteolysis as a possible route to iron mobilization, but the paper does not establish that stored iron is released on a minutes-long timescale; it also does not support reduction as a mobilization mechanism. (LLM, conf=0.83)

  Experimental — accuracy not yet measured

May combine two claims.

Bacterial cells exposed to Hg2+ sense this metal and mount a transcriptional response within minutes.

“bacterial cells exposed to Hg2+ sense this metal and mount a transcriptional response within minutes.209”

• cites [209] sourceSupported

May combine two claims.

Iron is redox active and very poorly soluble in the oxidized Fe3+ form, which has led to the evolution of high affinity iron-binding siderophores synthesized by many bacteria and fungi.

“Iron is redox active, and very poorly soluble in the oxidized Fe3+ (ferric) form, which has led to the evolution of high affinity iron-binding compounds (siderophores) synthesized by many bacteria and fungi.18,19”

• cites [18] sourcePartly supported

  The Introduction (page unavailable) says iron hydrate Fe(OH)3 is highly insoluble at physiological pH and that bacteria evolved high-affinity siderophores that increase iron’s water solubility. The passages do not establish the claim’s extension to fungi or explicitly describe iron as redox active. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [19] sourcePartly supported

  The Introduction (Iron in bacterial cellular metabolism; page unavailable) describes iron's accessible FeII and FeIII oxidation states. The sections on the intracellular fate of FeIII-siderophore complexes and general features and regulation say that reduction to FeII greatly increases aqueous solubility and that siderophores are high-affinity FeIII chelators; the paper also gives examples synthesized by bacteria. The passages do not establish siderophore synthesis by fungi or explicitly attribute the evolution of siderophores to ferric iron's poor solubility. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

May combine two claims.

Ribosomes can bind >500 Fe2+ ions, although these ribosomes were less functional than those reconstituted with Mn2+.

“Similarly, ribosomes can bind >500 Fe2+ ions, although these ribosomes were less functional than those reconstituted with Mn2+.”

• cites [70] sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Iron may also be stored by loading into dedicated membrane-bound organelles known as ferrosomes, but their biology is only beginning to be understood.

“Iron may also be stored by loading into dedicated membrane-bound organelles known as ferrosomes,134,135 but their biology is only beginning to be understood.”

• cites [134] sourceSupported
• cites [135] sourceSupported

May combine two claims.

Labile cation pools are sensed by metalloregulatory systems and serve to metalate nascent metalloproteins.

“The labile cation pools are sensed by metalloregulatory systems1,219 and serve to metalate nascent metalloproteins.3”

• cites [1] sourceSupported
• cites [219] sourceSupported
• cites [3] sourceSupported

May combine two claims.

The number of assigned Mg2+ ions varies widely, but in most cases Mg2+ is only sufficient to neutralize a fraction of the RNA charge, with the rest neutralized by ribosomal proteins and other cations.

“The number of assigned Mg2+ ions varies widely, but in most cases Mg2+ is only sufficient to neutralize a fraction of the RNA charge,65 with the rest neutralized by ribosomal proteins and other cations.”

• cites [65] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

If KM of 0.6 mM is a good proxy for Kd and binding is diffusion-limited (ka ~10^9 M^-1 s^-1), then maximal koff is 6 × 10^5 s^-1, corresponding to half-life ~1 ms.

“If the KM of 0.6 mM is a good proxy for the binding constant (Kd), and we postulate a reversible, diffusion-limited binding reaction (ka ∼ 109 M–1 s–1), we can estimate a maximal dissociation rate (koff) of 6 × 105 s–1 (where koff = Kd × kon), corresponding to half-life of ∼1 ms.”

• AssumptionThe authors state this as an assumption: KM of 0.6 mM is a good proxy for the binding constant (Kd).
• AssumptionThe authors state this as an assumption: Binding is a reversible, diffusion-limited reaction with ka ~10^9 M^-1 s^-1.

May combine two claims.

These displaced Mg2+ ions are exported from the cell, and the Mg2+-limited cell is unable to sustain translation.

“These displaced Mg2+ ions are exported from the cell, and the Mg2+-limited cell is unable to sustain translation.”

• cites [77] sourceNot checked yet

  Not checked in the free run.

May combine two claims.

B. subtilis RNase P binds ~150 Mg2+ ions with an apparent affinity (K1/2) of 0.26 mM Mg at low K+ (~50 mM K+), decreasing to a K1/2 of ~1.5 mM Mg2+ with higher K+ (~150 mM K+).

“For example, B. subtilis RNase P binds ∼150 Mg2+ ions with an apparent affinity (K1/2) of 0.26 mM Mg at low K+ (∼50 mM K+), decreasing to a K1/2 of ∼1.5 mM Mg2+ with higher K+ (∼150 mM K+).76”

• cites [76] sourceNot checked — no full text of the source

May combine two claims.

DNA and RNA polymerases function with multiple Mg2+ ions in their active site, with the highest affinity binding having a Kd of ~50-100 μM.

“DNA and RNA polymerases function with multiple Mg2+ ions in their active site,79 with the highest affinity binding having a Kd of ∼50–100 μM.80”

• cites [79] sourceNot checked — no full text of the source
• cites [80] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

MgtE functions as a Mg2+-gated channel and is feedback inhibited when intracellular Mg2+ reaches ~4 mM and binds to several cytoplasmic sensing sites.

“MgtE functions as a Mg2+-gated channel and is also feedback inhibited when intracellular Mg2+ reaches ∼4 mM and binds to several cytoplasmic sensing sites.74,75”

• cites [74] sourceNot checked — no full text of the source
• cites [75] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

At high external osmolarity, the more mobile water phase becomes depleted and the cytosol transitions to an immobile, glass-like state unable to support metabolic activity.

“At high external osmolarity, this more mobile water phase becomes depleted and the cytosol transitions to an immobile, glass-like state unable to support metabolic activity.”

May combine two claims.

Metal binding to metalloregulators often affects DNA affinity, and the converse is also true; these effects need to be considered when assessing sensitivity.

“Further, since metal binding to metalloregulators often affects DNA affinity, the converse is also true,26 and these effects need to be considered when assessing sensitivity.3,4”

• cites [26] sourceNot checked — no full text of the source
• cites [3] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

• cites [4] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

Sensitivity is determined by the affinity of the metalloregulator for its cognate ion and the effects of DNA-binding on metal affinity.

“Sensitivity is determined by the affinity of the metalloregulator for its cognate ion and the effects of DNA-binding on metal affinity (thermodynamic coupling), as discussed in detail elsewhere.26,30”

• cites [26] sourceNot checked — no full text of the source
• cites [30] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

The boundary between labile and sequestered metal pools is arbitrary, and sequestration can be conditional.

“The boundary between labile and sequestered metal pools is arbitrary, and sequestration can be conditional.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Water is obtained from the environment, but a significant fraction of cytosolic water can be generated by microbial catabolism, at least during rapid growth.

“Water is obtained from the environment, but a significant fraction of cytosolic water can be generated by microbial catabolism, at least during rapid growth.39”

• cites [39] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing).

The fraction of the K+ quota that is free or associated with low molecular weight ligands has been empirically defined as those ions released from cells when the membrane is transiently permeabilized by hypoosmotic shock.

“The fraction of the K+ quota that is free or associated with low molecular weight (LMW) ligands has been empirically defined as those ions released from cells when the membrane is transiently permeabilized by hypoosmotic shock.49”

• cites [49] sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

There is no shortage of metal ligands in the cell; ribosomes, RNA, DNA, proteins, nucleotides, amino acids, phospholipids, phosphosugars, and thiol-containing metabolites all play important roles.

“There is no shortage of metal ligands in the cell; ribosomes, RNA, DNA, proteins, nucleotides, amino acids, phospholipids, phosphosugars, and thiol-containing metabolites all play important roles.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The central role of K+ and Mg2+ as bulk ions, and of Mg2+ in enzyme catalysis, places these two elements among the dozen or so that are universally essential for life.

“The central role of K+ and Mg2+ as bulk ions, and of Mg2+ in enzyme catalysis, places these two elements among the dozen or so that are universally essential for life.9,44”

• cites [9] sourceNot checked — no full text of the source
• cites [44] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Zn2+ levels are often 10 μM to 1 mM, whereas copper quotas are variable but often lower than Zn2+.

“For the high affinity metals Zn2+ (light gray) levels are often 10 μM to 1 mM, whereas copper (brown) quotas are variable, but often lower than Zn2+.”

May combine two claims.

Within the complex milieu of the cytosol, the biochemically determined metal sensitivity of metalloregulatory proteins and metal-sensing riboswitches provides a useful proxy for free metal concentrations and defines the biological set-point for specific genetic changes.

“Within the more complex milieu of the cytosol, the biochemically determined metal sensitivity of metalloregulatory proteins and metal-sensing riboswitches provides a useful proxy3,4 and defines the biological set-point for specific genetic changes (Figure 2).4,24”

• cites [3] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

• cites [4] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

• cites [24] sourceNot checked — no full text of the source

May combine two claims.

Most manganese and iron is bound, but a small free pool is present and contributes to metal acquisition by nascent metalloproteins.

“Most manganese and iron is bound, but a small free pool is present and contributes to metal acquisition by nascent metalloproteins.3”

• cites [3] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

For some regulatory proteins there are multiple metal-binding sites in the functional oligomer and these may bind with negative cooperativity.

“For some regulatory proteins there are multiple metal-binding sites in the functional oligomer and these may bind with negative cooperativity.25”

• cites [25] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing).

Sequestered metals may become bioavailable due to metal ion competition, changes in redox state, export from vacuoles, or mobilization from storage reservoirs.

“For example, sequestered metals may become bioavailable due to metal ion competition, changes in redox state, export from vacuoles, or mobilization from storage reservoirs.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

K+ is hydrated with 6-8 or more loosely bound water molecules that exchange rapidly (picosecond time scale), and hydrated K+ ions form both inner and outer sphere ion pairs with cellular anions.

“K+ is hydrated with 6–8 or more loosely bound water molecules that exchange rapidly (picosecond time scale) and the hydrated K+ ions form both inner and outer sphere ion pairs with cellular anions (Figure 4).”

May combine two claims.

The metabolite pool is dominated by anions, with glutamate levels approaching 100 mM and substantial contributions from NTPs and other phosphorylated compounds.

“The metabolite pool is also dominated by anions, with glutamate levels approaching 100 mM and substantial contributions from NTPs and other phosphorylated compounds.43”

• cites [43] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The resulting metal complexes are often polydentate and include many metalloproteins and common cofactors.

“The resulting complexes are often polydentate and include the many metalloproteins in the cell as well as common cofactors (e.g., heme, chlorophyll, cobamides, molybdenum cofactor).”

Probably not a substantial claim: may not pass S4 (based). May combine two claims.

An initial picture has emerged of how metals are distributed at equilibrium during balanced growth, but capturing the magnitude and kinetics of metal redistribution in response to sudden metal depletion or excess has proven challenging.

“An initial picture has emerged of how metals are distributed at equilibrium during balanced growth, but capturing the magnitude and kinetics of metal redistribution in response to sudden metal depletion or excess has proven challenging.”

• AssumptionRests on an assumption: The precise nature of the labile metal pool is still not fully understood.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Studies in E. coli reveal dominant contributions from proteins (200-320 mg/mL) and RNA (75-120 mg/mL) with DNA present at lower levels (11-18 mg/mL).

“Studies in E. coli reveal dominant contributions from proteins (200–320 mg/mL) and RNA (75–120 mg/mL) with DNA present at lower levels (11–18 mg/mL).37”

• cites [37] sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

Manganese and iron have intermediate properties between highly available ions and ions with less than one free ion per bacterial cell.

“Manganese and iron have intermediate properties.”

• AssumptionRests on an assumption: Features of labile metal pools found in model systems such as Escherichia coli and Bacillus subtilis are broadly conserved across bacteria.

May combine two claims.

In E. coli approximately half (∼230 mM) of cytosolic K+ was found to be bound and the other half (∼250 mM) present in the released pool.

“In E. coli approximately half (∼230 mM) of cytosolic K+ was found to be bound and the other half (∼250 mM) present in the released pool.50”

• cites [50] sourceNot checked — no full text of the source

May combine two claims.

The physicochemical properties of the cell interior are vastly different from those of dilute aqueous solutions and are dominated by the high concentration of macromolecules that collectively occupy ∼30% of the cell volume.

“The physicochemical properties of the cell interior are vastly different from those of dilute aqueous solutions and are dominated by the high concentration of macromolecules that collectively occupy ∼30% of the cell volume.34−36”

• cites [34] sourceNot checked — no full text of the source
• cites [35] sourceNot checked — no full text of the source
• cites [36] sourceNot checked — no full text of the source

• AssumptionThe authors state this as an assumption: The interior of the cell can be approximated as an aqueous solution nearly saturated with large and complex biological polymers, metabolites, and ions.

Probably not a substantial claim: may not pass S3 (load-bearing).

The remainder of the cell volume (~50-70%) is water and dissolved solutes, including metabolites and inorganic ions.

“The remainder of the volume (∼50–70%) is water and dissolved solutes, including metabolites and inorganic ions.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Biochemical processes that support life largely play out in the crowded milieu of the cell interior.

“The biochemical processes that support life largely play out in the crowded milieu of the cell interior (Figure 3).33”

• cites [33] sourceNot checked — no full text of the source

Classified as probably not a substantial claim.

Within the intracellular environment, metal ions are present in a myriad of coordination environments that range from tightly bound (sequestered) to highly mobile (labile).

“Within the intracellular environment, metal ions are present in a myriad of coordination environments that range from tightly bound (sequestered) to highly mobile (labile) (Figure 1).”

May combine two claims.

For regulators of metal import, the set-point defines the boundary between metal deficiency and sufficiency, whereas for regulators of efflux and storage, the set-point delineates the boundary between sufficiency and excess.

“For regulators of metal import, the set-point defines the boundary between metal deficiency and sufficiency, whereas for regulators of efflux and storage, the set-point delineates the boundary between sufficiency and excess.1”

• cites [1] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

These free metal concentration values are comparable to those for other species.

“These values are comparable to those for other species.”

Probably not a substantial claim: may not pass S3 (load-bearing).

One major function of the aqueous phase is the solvation of macromolecules, metabolites, and ions.

“One major function of this aqueous phase is the solvation of macromolecules, metabolites, and ions.40”

• cites [40] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

In the crowded cell environment, water serves as both solvent and metabolite.

“In this crowded, jostling environment, water serves as both solvent and metabolite.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Intracellular manganese is often bound to specific metalloenzymes, including mononuclear manganese enzymes and those with more complex arrangements that may involve other metals.

“Intracellular manganese is often bound to specific metalloenzymes, including mononuclear manganese enzymes and those with more complex arrangements that may involve other metals.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

K+ is the single most abundant ion in the cell.

“In sum, K+ is the single most abundant ion in the cell with large and rapidly exchanging pools of free (hydrated) ions and labile complexes with both macromolecules (e.g., nucleic acids, proteins) and metabolites.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Bound manganese can serve as an electrophilic center or in redox reactions.

“Bound manganese can serve as an electrophilic center or in redox reactions.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Ribosome structures can now be determined to better than 2 Å resolution using cryo-electron microscopy (cryo-EM).

“Ribosome structures can now be determined to better than 2 Å resolution using cryo-electron microscopy (cryo-EM).67”

• cites [67] sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Manganese and iron have a moderate affinity for ligands, as seen in the Irving-Williams series.

“Manganese (Mn) and iron (Fe) have a moderate affinity for ligands, as seen in the Irving-Williams series.”

• AssumptionRests on an assumption: The Irving-Williams series ordering of metal-ligand affinities applies to the intracellular ligands and conditions discussed.

May combine two claims.

The large pools of K+ and Mg2+ associated with ribosomes, other nucleic acids, and metabolites overlap in their binding sites, which can lead to physiological consequences.

“The large pools of K+ and Mg2+ associated with ribosomes (Figure 4), other nucleic acids, and metabolites overlap in their binding sites, which can lead to interesting physiological consequences.”

May combine two claims.

These concentrations serve as a signal of Mg2+ sufficiency and reveal the homeostatic set-point for free Mg2+.

“These concentrations thereby serve as a signal of Mg2+ sufficiency and reveal the homeostatic set-point for free Mg2+ (Figure 2).”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

The large respiratory complex contains abundant iron and is a major destination for copper.

“The large respiratory complex (motm/273) contains abundant iron and is a major destination for copper.”

May combine two claims.

Accurate metal assignments are not trivial, and even structures determined by X-ray crystallography have had metals assigned incorrectly.

“However, accurate metal assignments are not trivial, and even structures determined by X-ray crystallography (where anomalous scattering can provide relevant information) have had metals assigned incorrectly.68”

• cites [68] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

In cyanobacteria and other phototrophs, intracellular membranes contain abundant chlorophyll (Mg), and PSII contains the Mn,Ca-containing oxygen-evolving complex.

“In cyanobacteria and other phototrophs, intracellular membranes contain abundant chlorophyll molecules (Mg), and PSII additionally contains the Mn,Ca-containing oxygen-evolving complex (motm/59).”

Probably not a substantial claim: may not pass S3 (load-bearing).

This sequestered iron is conditionally mobilized in response to iron deprivation.

“This sequestered iron is conditionally mobilized in response to iron deprivation.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

One common mechanism for Mg2+ storage is membrane-bound vacuoles, as seen in S. cerevisiae and higher plants, but this mechanism has not been documented in bacteria.

“One common mechanism for Mg2+ storage is membrane-bound vacuoles, as seen in S. cerevisiae and higher plants,78 but this mechanism has not been documented in bacteria.”

• cites [78] sourceNot checked — no full text of the source

May combine two claims.

Cell envelope-associated Mg2+ serves as a counterion for membrane phospholipids and lipopolysaccharides in Gram-negative bacteria and can account for 1/3 of the Mg2+ quota.

“Cell envelope-associated Mg2+ serves as a counterion for membrane phospholipids and lipopolysaccharides in Gram-negative bacteria and this can account for 1/3 of the quota (Figure 3).60”

• cites [60] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Classified as probably not a substantial claim.

These values are based on analyses of ribosomes crystallized from a solution high in K+ (100 to 200 mM KSCN) and lacking Mg2+.

“Of note, these values are based on analyses of ribosomes crystallized from a solution high in K+ (100 to 200 mM KSCN) and lacking Mg2+.”

May combine two claims.

The reaction catalyzed by Mg2+ chelatase is unfavorable (Keq ∼ 10-6) and is coupled to ATP hydrolysis.

“The reaction catalyzed by Mg2+ chelatase is unfavorable (Keq ∼ 10–6) and is coupled to ATP hydrolysis.84”

• cites [84] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

Once synthesized, chlorophyll-Mg complexes are stable, with spontaneous Mg2+ loss occurring with a half-time of ∼6 h, and are therefore no longer part of the labile pool.

“Once synthesized, chlorophyll-Mg complexes are stable (spontaneous Mg2+ loss occurs with a half-time of ∼6 h),84 and therefore no longer part of the labile pool.”

• cites [84] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

May combine two claims.

The structure of the 70S ribosome from Thermus thermophilus has >3000 modeled cations, all but 3 initially assigned as Mg2+.

“The structure of the 70S ribosome from Thermus thermophilus (PDB 4 V6F)51 has >3000 modeled cations (c). All but 3 of these were initially assigned as Mg2+.”

• cites [51] sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Metals in large complexes are generally considered to be sequestered.

“Metals in these large complexes are generally considered to be sequestered.”

Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

Because inner sphere coordination sites often involve only 2 to 3 ligands from the ribosome, it is possible that many of these sites can accommodate either Mg2+ or K+, depending on ambient levels in the cell.

“Since even the inner sphere coordination sites often involve only 2 to 3 ligands from the ribosome, it is possible that many of these sites can accommodate either Mg2+ or K+, depending on the ambient levels in the cell.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Aconitase contains a 4Fe4S cluster that can reversibly lose iron in response to oxidative stress or iron depletion.

“Aconitase (motm/89) contains a 4Fe4S cluster that can reversibly lose iron in response to oxidative stress or iron depletion.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Mg2+ is the most abundant divalent cation in cells (quota ~100 mM).

“Mg2+ is the most abundant divalent cation in cells (quota ∼100 mM) and plays a central role in nucleic acid structure and as an enzyme cofactor.5”

• cites [5] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The smaller Mg2+ ion (radius ∼0.72 Å) typically has 6 oxygen ligands, whereas the larger K+ ion (radius ∼1.5 Å) has more variable coordination, with 8 ligands common.

“The smaller Mg2+ ion (green; radius ∼0.72 Å) typically has 6 oxygen (red) ligands (a), whereas the larger K+ ion (magenta; radius ∼1.5 Å) has more variable coordination, with 8 ligands common (b).”

May combine two claims.

Both manganese and iron are critical nutrients for most bacteria.

“Although both are critical nutrients for most bacteria, the cellular quotas for these metals are variable and typically <1 mM,11 a value ∼100-fold lower than K+ and Mg2+ (≥100 mM).”

• cites [11] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Surface-associated K+ ions are labile, whereas those at subunit interfaces may be sequestered during the translation cycle and then labile when subunits dissociate, and others deeper within subunit structures may be sequestered on a longer time scale.

“Conceptually, we can anticipate that surface-associated K+ ions are labile, whereas those at the subunit interfaces may be sequestered during translation cycle and then labile when the subunits dissociate, and others deeper within the subunit structures may be sequestered on a longer time scale.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

The only widespread mechanism in biology for partitioning K+ (and related Na+) ions into a stored form requires membrane partitioning.

“More broadly, the only widespread mechanism in biology for the partitioning of K+ (and related Na+) ions into a “stored” form requires membrane partitioning.”

• AssumptionRests on an assumption: In animal cells, the sodium–potassium ATPase maintains transmembrane gradients that serve in secondary active transport and nerve conduction.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Mg2+ plays a central role in nucleic acid structure and as an enzyme cofactor.

“Mg2+ is the most abundant divalent cation in cells (quota ∼100 mM) and plays a central role in nucleic acid structure and as an enzyme cofactor.5”

• cites [5] sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Growth in the absence of iron imposes considerable metabolic restrictions, including a lack of respiratory chains and other heme-containing enzymes.

“Growth in the absence of iron imposes considerable metabolic restrictions, including a lack of respiratory chains and other heme-containing enzymes.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The crystallization conditions in both 70S ribosome studies contained at least 100 mM KSCN and no added Mg2+ ions.

“Note that the crystallization conditions in both studies contained at least 100 mM KSCN and no added Mg2+ ions.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Ferritins are hollow, spherical molecules with 24 identical subunits that oxidize and store iron in their hollow interior.

“Ferritins (motm/35) are hollow, spherical molecules with 24 identical subunits that oxidize and store iron in their hollow interior.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

MnSOD contributes a significant fraction of the cytosolic Mn2+ pool.

“MnSOD contributes a significant fraction of the cytosolic Mn2+ pool.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.