Infrared spectroscopy of proteins

“Only the strongest bands are listed in Table 1, or 724 – 1174 Couples with adjacent CH 2 groups, in phase mode at 724 cm − 1 most intense [79] Extended and corrected version of a previous compilation [150].”

“Examples are (i) the two coupled CO vibrations in the COO − group which make the carboxylate absorption sensitive to the mode of cation chelation [95 – 97] and has been used in studies of several Ca 2+ binding proteins [98,99]; (ii) the sensitivity of P \ O or V \ O stretching vibrations of…”

“The two most common approaches to determine the secondary structure are: (i) fitting the amide I band with component bands [10,220,228] after identifying their position with band narrowing techniques [229 – 232] and (ii) decomposing the amide I band into basis spectra which have been calculated…”

“The amide II band is weak or absent in the Raman spectrum [151].”

“Probably the most common application of infrared spectroscopy in protein studies is the analysis of secondary structure [1,3,4,6,8 – 10, 221, 222 ].”

“Only the strongest bands are listed in Table 1, or 724 – 1174 Couples with adjacent CH 2 groups, in phase mode at 724 cm − 1 most intense [79] Extended and corrected version of a previous compilation [150].”

“Thus every encounter of an acidic side chain group with OH − will abstract the side chain proton while on average 1000 collisions are needed to deprotonate an amide group [250].”

“…structure are: (i) fitting the amide I band with component bands [10,220,228] after identifying their position with band narrowing techniques [229 – 232] and (ii) decomposing the amide I band into basis spectra which have been calculated from a calibration set of spectra from proteins with…”

“…effects: (i) Exciton transfer : if energy is absorbed by an oscillator it does not remain there but is rather transferred to a nearby oscillator with a typical time constant of 0.5 ps for an α - helix [178] — as a consequence the excited state is delocalised, typically over a length of 8 Å [178].”

“This information has been evaluated [93] using a correlation between P \ O frequency and P \ O bond valence [100], the bond valence model [85,421] and empirical correlations to calculate P \ O bond strengths, P \ O bond lengths, and finally the dissociation energy of the bridging P \ O bond.”

“The results are in line with the proposed role of this residue in proton pumping by mammalian oxidases [407].”

“The symmetric and antisymmetric stretching vibrations of non-hydrogen bonded water absorb between 3630 and 3760 cm − 1 [274,277,292 – 296], whereas bonded OH groups absorb between 3600 and 2900 cm − 1 depending on the strength and pattern of hydrogen bonding [274,277,295].”

“Hydration of proteins has been studied by infrared spectroscopy as reviewed previously [276,278].”

“This makes infrared spectroscopy a valuable tool for the investigation of protein structure [1 – 11] of the molecular mechanism of protein reactions [2,10 – 35] and Further advantages of infrared spectroscopy are a large application range from small soluble proteins to large membrane proteins, a…”

“Protonated water clusters give rise to a particular absorption spectrum that depends critically on the number of water molecules over which the proton is delocalised [297].”

“The attenuated total reflectance (ATR) technique [26,124 – 126] is illustrated in Fig.”

“Infrared spectroscopy of liquid water [274 – 276] and water clusters [277] has been reviewed recently.”

“For protein samples, usually a protein film is prepared on the crystal surface [121,125,127,128], often simply by drying, and a buffer is placed on top of the film.”

“…[79], Arg, Asn [152,154,155,424], Asp [152,154,155,432,433], Cys [434], Gln [152,154,155,435], Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr [79,438], Trp, [162,430,440,441], Tyr…”

“For the quantitative evaluation of band shifts induced by hydrogen bonding Badger and Bauer relationships [108] are often used.”

“…a cuvette that is held at a different temperature (time resolution 100 ms) [241,243], by a laser pulse near 2 μ m that is absorbed by the sample solvent 2 H 2 O [40,43,324,325] (temperature maximum reached after 20 ns [43]) or by a visible laser pulse that excites a heat transducing dye [326,327].”

“Its proton is transferred to Asp-85 upon formation of the M intermediate [380,385,387,396] as identified by mutation of this residue [385,387].”

“…vibration References: aliphatic groups [79], Arg, Asn [152,154,155,424], Asp [152,154,155,432,433], Cys [434], Gln [152,154,155,435], Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr…”

“A striking example is the possibility to identify bacterial strains from the infrared spectrum and to differentiate and classify microorganisms [45].”

“The table is based on the experimental data and assignments of various authors collected and evaluated by Goormaghtigh et al. [6].”

“This has later been confirmed by X-ray crystallography [417,418].”

“The error can be slightly reduced, and a prediction of the 3 10 -helix content included, by using three, but not more, wavenumbers specifically for each secondary structure [240].”

“[36–38,43,44,241–246] and the topic has been reviewed [7,43,244].”

“This has later been confirmed by X-ray crystallography [417,418].”

“In particular, the isolated (i.e. non-solvated) Eigen cation H 3 O + (H 2 O) 3 has a characteristic absorption at 2665 cm − 1 (OH stretch) [297,298] and the isolated Zundel cation H 2 O ⋯ H + ⋯ OH 2 near 1750 cm − 1 (HOH bend) and 1050 cm − 1 (O ⋯ H + ⋯ O stretch or bend) [297,299].”

“One drawback of infrared spectroscopy of aqueous solutions is the strong absorbance of water in the mid-infrared spectral region (near 1645 cm − 1 ) [120] which overlaps the important amide I band of proteins and some side chain bands (see below).”

“This can be used to separate the amide I bands of two proteins or a protein and a peptide for binding studies [369,370], to probe the local secondary structure of peptides [188,211,371 – 375] or to determine band shifts due to hydrogen bonding to water [194,195].”

“There is evidence for some through-bond coupling between nearest neighbours from ab initio calculations on NMA [184] and di-and tripeptides [185 – 187] and from semiempirical calculations on larger peptides [188].”

“This simple approach can explain the general features of amide I absorbance of secondary structures [173 – 176 (ii) For calculating the amide I band of proteins, a “ floating oscillator model ” has been developed [203,204].”

“In spite of side chain contributions to the amide III mode, this mode can be used for secondary structure prediction [166 – 169].”

“This simple approach can explain the general features of amide I absorbance of secondary structures [173 – 176 (ii) For calculating the amide I band of proteins, a “ floating oscillator model ” has been developed [203,204].”

“However, as discussed above, similar spectra are expected for finite or twisted β -sheets [175,176,203,212] and there is no experimental evidence for a difference between the frequencies of parallel and antiparallel β -sheet [218,220].”

“Table 1 gives an overview of the infrared absorption of amino acid side chains in 1 H 2 O and 2 H 2 O [11,150], see also further compilations of infrared bands [4,151 – 156] and of Raman bands [157 – 162].”

“…importance was the identification of the proton transporting groups from the early detection of protonated carboxyl groups [376,378] to the assignment to specific residues or a localised protonated water cluster using isotopic labeling [384 – 386] and site-directed mutagenesis [307,385 – 388].”

“The result is a splitting of the amide I band, which can be as large as ∼ 70 cm − 1 [179,180] for β -sheet structures.”

“Here, continuous illumination or a light flash induces a reaction in photosensitive proteins like bacteriorhodopsin [14 – 17] or photosynthetic reaction centers [12,13,21,22].”

“The symmetric and antisymmetric stretching vibrations of non-hydrogen bonded water absorb between 3630 and 3760 cm − 1 [274,277,292 – 296], whereas bonded OH groups absorb between 3600 and 2900 cm − 1 depending on the strength and pattern of hydrogen bonding [274,277,295].”

“Nevertheless it has led to interesting insight [29,174 – 176,203 , 204 ,206 ] (iii) A normal mode analysis can be carried out using a simplified general valence force field for the polypeptide with that of N -methylacetamide serving as a starting point [151].”

“Infrared investigations became available with the development of an ultra-thin-layer spectroelectrochemical cell suitable for protein investigations in aqueous solution [330].”

“Its proton is transferred to Asp-85 upon formation of the M intermediate [380,385,387,396] as identified by mutation of this residue [385,387].”

“In deuterated proteins up to 10 cm lower [155,424] HisH2 , ν(C_C) 1631 (250) 1600 (35), 1623 (16) Only one strong band observed for 4-methylimidazole at 1633 (H2O) and 1605 cm −1 ((2)H2O) [426] Lys, δas(NH3 ) 1626–1629 (60–130) 1201 (2)H2O band position based on shift observed for CH3NH3Cl and CH3N (2)H3Cl Tyr-OH, ν(C…”

“This notion of infrared spectroscopy being a marker-free technique has recently received an interesting twist in a study that reported a genetically encoded CN infrared label which was used to probe ligand binding to myoglobin [50].”

“Pressure-jump experiments [328,329] require a cell that allows to set the sample under pressures of several kbar and have an experimental dead time of about 20 s. Equilibrium electrochemistry can be used to initiate redox reactions of proteins.”

“All techniques mentioned and biological or photochemical applications thereof have been reviewed before [20,23,133 – 143].”

“The models differ as to whether the electric effects of the environment on a given amide group are accounted for by the electric potential [197 – 199], the electric field [200], or a combination of electric field and its derivatives [113,201].”

“A promising technique to further reduce the amount of material is surface-enhanced infrared spectroscopy [123] — the infrared analog of surface enhanced Raman spectroscopy.”

“…made it possible to apply time-resolved techniques like single wavelength measurements with a global source [377 – 379], stroboscopic FTIR spectroscopy [380,381] and the step scan technique [144,382,383] which require numerous repetitions of the flash-induced experiment on a single sample.”

“Motional narrowing can counteract the effects of a heterogeneous environment for amide groups that are hydrogen bonded to bulk water [111 – 113].”

“The models differ as to whether the electric effects of the environment on a given amide group are accounted for by the electric potential [197 – 199], the electric field [200], or a combination of electric field and its derivatives [113,201].”

“This can be used to separate the amide I bands of two proteins or a protein and a peptide for binding studies [369,370], to probe the local secondary structure of peptides [188,211,371 – 375] or to determine band shifts due to hydrogen bonding to water [194,195].”

“Motional narrowing can counteract the effects of a heterogeneous environment for amide groups that are hydrogen bonded to bulk water [111 – 113].”

“Only with the introduction of the transition dipole coupling mechanism [170] this splitting in a main band near 1630 cm − 1 and a side band near 1690 cm − 1 could be explained.”

“Examples for infrared spectroscopic measurements of enzyme activity are cefoxitin hydrolysis by β -lactamase [77], deacylation of cinnamoyl-chymotrypsin [78], ATP hydrolysis by the Ca 2+ - ATPase [72], oxidation of D -glucose by glucose oxidase [74], hydrolysis of amides [76,273], synthesis of…”

“Several of the approaches have been compared and shown to yield similar results for NMA in water ( 2 H 2 O) [200], but for the intramolecular interaction within small peptides, the correlation between frequency and electric potential works best [196].”

“An acidic aqueous solution exhibits a broad continuous absorption between 1000 and 3100 cm − 1 and additional bands with respect to neutral water near 1200, 1740, and 2900 cm − 1 [269,300 – 303] consistent with the presence of both, the Eigen and the Zundel forms of the hydrated proton [303].”

“Instead, the protein reaction of interest has to be initiated directly in the cuvette and the associated infrared absorbance changes can be recorded [2,10,20,23,135].”

“In consequence, the high-wavenumber side band is often, but not always, absent for parallel β -sheets [217 – 219].”

“An acidic aqueous solution exhibits a broad continuous absorption between 1000 and 3100 cm − 1 and additional bands with respect to neutral water near 1200, 1740, and 2900 cm − 1 [269,300 – 303] consistent with the presence of both, the Eigen and the Zundel forms of the hydrated proton [303].”

“Table 1 gives an overview of the infrared absorption of amino acid side chains in 1 H 2 O and 2 H 2 O [11,150], see also further compilations of infrared bands [4,151 – 156] and of Raman bands [157 – 162].”

“Infrared spectroscopy has detected protonated water clusters in proteins, for example in a bacterial reaction centre [302] and in bacteriorhodopsin [304 – 307], where the localisation of the proton is affected by mutation of nearby amino acids [307].”

“The exchange characteristics of proteins might depend on their particular physiological state and can be modulated by the binding of ligands [257,258], during catalysis [259] or by interaction with membranes [260].”

“The combination of explicit water molecules in the first hydration shell and of a continuum model for water reproduces the experimentally observed shifts [190,191].”

“The models differ as to whether the electric effects of the environment on a given amide group are accounted for by the electric potential [197 – 199], the electric field [200], or a combination of electric field and its derivatives [113,201].”

“Nevertheless it provides valuable structural information and secondary structure prediction can be done with the amide II band alone [165].”

“Probably the most common application of infrared spectroscopy in protein studies is the analysis of secondary structure [1,3,4,6,8 – 10, 221, 222 ].”

“…aliphatic groups [79], Arg, Asn [152,154,155,424], Asp [152,154,155,432,433], Cys [434], Gln [152,154,155,435], Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr [79,438], Trp,…”

“…a cuvette that is held at a different temperature (time resolution 100 ms) [241,243], by a laser pulse near 2 μ m that is absorbed by the sample solvent 2 H 2 O [40,43,324,325] (temperature maximum reached after 20 ns [43]) or by a visible laser pulse that excites a heat transducing dye [326,327].”

“Probably the most common application of infrared spectroscopy in protein studies is the analysis of secondary structure [1,3,4,6,8 – 10, 221, 222 ].”

“This has been done by carefully subtracting the spectrum of a sample where the protein is in state B from a spectrum where it is in state A [262,264 – 271].”

“They have been reviewed before [2,14,15,18,20,24,25,27,28,30] and are only briefly discussed here.”

“Protein cofactors have also been labeled for example for bacteriorho-dopsin [17,362], photosynthetic reaction centres [12,13,22] and cytochrome c oxidase [335].”

“Vibrations dominated by amide group motions are not included. ν stretching vibration, ν s: symmetric stretching vibration, ν as : antisymmetric stretching vibration, δ : in plane bending vibration, δ as : asymmetric in plane bending vibration, γ w : wagging vibration, γ t : twisting vibration, γ r : rocking vibration…”

“The models differ as to whether the electric effects of the environment on a given amide group are accounted for by the electric potential [197 – 199], the electric field [200], or a combination of electric field and its derivatives [113,201].”

“An example is Asp-96 of bacteriorhodopsin for which a p K a N 12 has been found [163].”

“…the amide I band with component bands [10,220,228] after identifying their position with band narrowing techniques [229 – 232] and (ii) decomposing the amide I band into basis spectra which have been calculated from a calibration set of spectra from proteins with known structure [10,233 – 238].”

“Its proton is transferred to Asp-85 upon formation of the M intermediate [380,385,387,396] as identified by mutation of this residue [385,387].”

“Combining this knowledge from infrared spectroscopy with that from recent structures at atomic resolution “ the path of the proton through the membrane can now be followed in exquisite detail ” [389].”

“The result is a splitting of the amide I band, which can be as large as ∼ 70 cm − 1 [179,180] for β -sheet structures.”

“This approach has been used in studies of the Ca 2+ -ATPase pump mechanism [349] of the photoactive yellow protein photocycle [350], and of protein folding studies [36,38,42,43].”

“The fundamental mechanism that renders the amide I vibration sensitive to secondary structure is transition dipole coupling (TDC) [170,173 – 177].”

“While much of the initial work has been on photosynthetic proteins (see references above), recent work has concentrated on cytochrome c oxidases [32,333 – 340].”

“The retinal Schiff base remains protonated in the early phase of the photocycle [391].”

“The effects of hydrogen bonding on the infrared spectrum of NMA have been examined computationally in ab initio calculations and experimentally [171,189 – 191].”

“Parallel β -sheets [173,175] have their main absorption at higher wavenumber than corresponding antiparallel β -sheets [173,176] although the difference can be as little as 4 cm − 1 [217] and the parallel β -sheet band can be as low as 1622 cm − 1 (in H 2 O) for β -barrel proteins [218] and as low…”

“Of particular importance was the identification of the proton transporting groups from the early detection of protonated carboxyl groups [376,378] to the assignment to specific residues or a localised protonated water cluster using isotopic labeling [384 – 386] and site-directed mutagenesis…”

“Already in 1981, CO photodissociation experiments have led to significant conclusions regarding the catalytic centre [402].”

“This can be used to separate the amide I bands of two proteins or a protein and a peptide for binding studies [369,370], to probe the local secondary structure of peptides [188,211,371 – 375] or to determine band shifts due to hydrogen bonding to water [194,195].”

“At short distances ( b 6 Å [181]) the TDC approximation becomes less satisfactory [181 – 183].”

“Table 1 gives an overview of the infrared absorption of amino acid side chains in 1 H 2 O and 2 H 2 O [11,150], see also further compilations of infrared bands [4,151 – 156] and of Raman bands [157 – 162].”

“This can be used to separate the amide I bands of two proteins or a protein and a peptide for binding studies [369,370], to probe the local secondary structure of peptides [188,211,371 – 375] or to determine band shifts due to hydrogen bonding to water [194,195].”

“This can be used to separate the amide I bands of two proteins or a protein and a peptide for binding studies [369,370], to probe the local secondary structure of peptides [188,211,371 – 375] or to determine band shifts due to hydrogen bonding to water [194,195].”

“In particular, the isolated (i.e. non-solvated) Eigen cation H 3 O + (H 2 O) 3 has a characteristic absorption at 2665 cm − 1 (OH stretch) [297,298] and the isolated Zundel cation H 2 O ⋯ H + ⋯ OH 2 near 1750 cm − 1 (HOH bend) and 1050 cm − 1 (O ⋯ H + ⋯ O stretch or bend) [297,299].”

“These quantities are calculated at two [199] or four [113,198 – 200] atoms of the amide group, at six atoms of NMA [197,200], or at up to 65 sites of the amide group [201] and related to the amide I frequency via ab initio quantum chemical calculations.”

“For protein samples, usually a protein film is prepared on the crystal surface [121,125,127,128], often simply by drying, and a buffer is placed on top of the film.”

“This makes infrared spectroscopy a valuable tool for the investigation of protein structure [1 – 11] of the molecular mechanism of protein reactions [2,10 – 35] and Further advantages of infrared spectroscopy are a large application range from small soluble proteins to large membrane proteins, a…”

“Of particular importance was the identification of the proton transporting groups from the early detection of protonated carboxyl groups [376,378] to the assignment to specific residues or a localised protonated water cluster using isotopic labeling [384 – 386] and site-directed mutagenesis…”

“As bond strength and bond length are directly related [59,84 – 86], bond distortions smaller than 1 pm in the course of a catalytic reaction can be monitored with astonishing accuracy.”

“…the amide I band with component bands [10,220,228] after identifying their position with band narrowing techniques [229 – 232] and (ii) decomposing the amide I band into basis spectra which have been calculated from a calibration set of spectra from proteins with known structure [10,233 – 238].”

“These molecules are termed caged compounds and have been used for 30 years to study biological reactions [311 – 317].”

“These experiments provide spatially resolved information about functionally important water molecules, for example in bacteriorhodopsin [16,282 – 287], rhodopsin [16,283,288], sensory rhodopsin [289], photo-system II [290] and cytochrome c oxidase [291].”

“Infrared spectroscopy of liquid water [274 – 276] and water clusters [277] has been reviewed recently.”

“…groups [79], Arg, Asn [152,154,155,424], Asp [152,154,155,432,433], Cys [434], Gln [152,154,155,435], Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr [79,438], Trp, [162,430,440,441], Tyr…”

“However, as discussed above, similar spectra are expected for finite or twisted β -sheets [175,176,203,212] and there is no experimental evidence for a difference between the frequencies of parallel and antiparallel β -sheet [218,220].”

“These have been outlined and tested against quantum chemical calculations of peptides [187,208,209].”

“An acidic aqueous solution exhibits a broad continuous absorption between 1000 and 3100 cm − 1 and additional bands with respect to neutral water near 1200, 1740, and 2900 cm − 1 [269,300 – 303] consistent with the presence of both, the Eigen and the Zundel forms of the hydrated proton [303].”

“This is illustrated well by model studies on isolated biological cofactors involved in photosynthesis [80 – 83] that allowed the assignment of signals in the protein spectra to specific molecular groups of the cofactors and in consequence statements about their protein environment [12,13, 21,22].”

“More information on this method can be found in reviews [12,21,30,32].”

“An alternative assignment of the amide B band to the stretching vibration of intramolecularly hydrogen bonded NH groups has recently found experimental support [164].”

“…made it possible to apply time-resolved techniques like single wavelength measurements with a global source [377 – 379], stroboscopic FTIR spectroscopy [380,381] and the step scan technique [144,382,383] which require numerous repetitions of the flash-induced experiment on a single sample.”

“Recently, a number of flow cells have been developed that enable mixing experiments [36,117 – 119].”

“…Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr [79,438], Trp, [162,430,440,441], Tyr [64,66,67,152,154,155,442,443]. those in a spectral window free of overlap by bands from other groups.”

“This approach has been used in studies of the Ca 2+ -ATPase pump mechanism [349] of the photoactive yellow protein photocycle [350], and of protein folding studies [36,38,42,43].”

“For α -helices there is also evidence for an effect of hydrogen bonding on the vibrational frequency since solvated helices (i.e. helices forming hydrogen bonds also to solvent molecules) absorb approximately 20 cm − 1 lower than non-solvated helices [40,192 – 195].”

“In addition to these effects, which are discussed below, changing the dielectric constant of the environment from 1 to 80 (water) reduces the calculated frequency for NMA by 30 cm − 1 [171] as suggested earlier for protein amide groups [172].”

“…and proteins are investigated, as illustrated by studies on the binding of CO [264] and O 2 [357] to hemoglobin, of O 2 [357] to myoglobin, of carbonyl groups to triosephosphate isomerase [266] and phospholipase A 2 [358], and of phosphate groups to Ras [91,114,359,360] and Ca 2+ -ATPase [361].”

“Cytochrome c oxidases and related heme-copper oxidases have been studied with a variety of infrared spectroscopic techniques as reviewed previously [32] including photodissociation of carbon monoxide (CO) [402], electrochemistry [334], photoreduction [345] and ATR spectroscopy [403,404].”

“In Raman studies [54], favourable binding enthalpies with respect to water as large as − 60 kJ/mol have been detected for C _ O groups of substrates bound to enzymes.”

“The band position of the main band shifts down with increasing helix length [174], when the helix is bent in coiled coils [192,213] and when the helix is solvent exposed (absorption maximum at 1640 – 1650 cm − 1 in H 2 O, at 1629 – 1640 cm − 1 in 2 H 2 O) [180,214 – 216].”

“Infrared spectroscopy has detected protonated water clusters in proteins, for example in a bacterial reaction centre [302] and in bacteriorhodopsin [304 – 307], where the localisation of the proton is affected by mutation of nearby amino acids [307].”

“Nevertheless, successful applications of mixing devices have been reported, as reviewed recently [244], first with the larger pathlength of 50 μ m for 2 H 2 O [118] and subsequently with 20 μ m [117] and around 10 μ m for 1 H 2 O [36,119].”

“Hydrogen bonding to PO 2 − groups lowers the observed band position of the symmetric stretching vibration by 3 to 20 cm − 1 and of the antisymmetric stretching vibration by 20 – 34 cm − 1 [104 – 107] with a single hydrogen bond contributing 16 cm − 1 in a nitrogen matrix [107].”

“…Glu [154,155,432,433], His − [65,426], HisH [65,154,426], HisH 2+ [64,65,155], Lys [152,154,427], Phe [154], Pro [429,436,437], Ser [79,434,438,439], Thr [79,438], Trp, [162,430,440,441], Tyr [64,66,67,152,154,155,442,443]. those in a spectral window free of overlap by bands from other groups.”

“…the carboxylate absorption sensitive to the mode of cation chelation [95 – 97] and has been used in studies of several Ca 2+ binding proteins [98,99]; (ii) the sensitivity of P \ O or V \ O stretching vibrations of phosphates or vanadates on the bond angle [100], applied to myosin [89] and Ras…”

“Amino acid side chains have a number of characteristic normal modes in the mid infrared (Venyaminov and Kalnin 1990a; Barth 2007).”

“1253 cm¡1, His’ v(CN) and d(CH) at 1104, 1090, 1106, and 1094 cm¡1, Thr’s n(CO) at 1075–1150 cm¡1 (NC) at 1092 cm¡1, Ser’s v(CO) or v(CC) at 983 cm¡1, v(NC), d(CH), and v(CC) at 1064 cm¡1, gt CH2 at 1063–1295 cm¡1, v(CC) and d (CH) at 1012–1016 cm¡1 (157).”