Cited by 177Retinal Development and DisordersRetinoids in leukemia and cellular processesPhotoreceptor and optogenetics research

Key enzymes of the retinoid (visual) cycle in vertebrate retina

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Kiser, Philip D., Golczak, Marcin, Maeda, Akiko, Palczewski, Krzysztof·2012·Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids

Abstract

A major goal in vision research over the past few decades has been to understand the molecular details of retinoid processing within the retinoid (visual) cycle. This includes the consequences of side reactions that result from delayed all-trans-retinal clearance and condensation with phospholipids that characterize a variety of serious retinal diseases. Knowledge of the basic retinoid biochemistry involved in these diseases is essential for development of effective therapeutics. Photoisomerization of the 11-cis-retinal chromophore of rhodopsin triggers a complex set of metabolic transformations collectively termed phototransduction that ultimately lead to light perception. Continuity of vision depends on continuous conversion of all-trans-retinal back to the 11-cis-retinal isomer. This process takes place in a series of reactions known as the retinoid cycle, which occur in photoreceptor and RPE cells. All-trans-retinal, the initial substrate of this cycle, is a chemically reactive aldehyde that can form toxic conjugates with proteins and lipids. Therefore, much experimental effort has been devoted to elucidate molecular mechanisms of the retinoid cycle and all-trans-retinal-mediated retinal degeneration, resulting in delineation of many key steps involved in regenerating 11-cis-retinal. Three particularly important reactions are catalyzed by enzymes broadly classified as acyltransferases, short-chain dehydrogenases/reductases and carotenoid/retinoid isomerases/oxygenases. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

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Crossref · 10.1016/j.bbalip.2011.03.005

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  • Only retinol dehydrogenases contribute to vision-related retinoid metabolism.

    “However, only RDH’s contribute to vision-related metabolism of retinoids.”

    From Chemistry of the Retinoid (Visual) Cycle (2014) · cites this paper as [287]

    Section 3 says RDHs catalyze two reactions in the visual retinoid cycle, but the claim's 'only' is contrary to the paper. Section 2.4 calls LRAT indispensable to that cycle and says LRAT and RPE65 are required for 11-cis-retinoid production in the RPE. Page numbers are unavailable in our copy. (LLM, conf=0.94)

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  • In visual phototransduction, large quantities of vitamin A in the form of 11-cis-retinal are isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal.

    “In this process, large quantities of vitamin A in the form of 11-cis-retinal are being isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal.”

    From The Role of Vitamin A in Retinal Diseases (2022) · cites this paper as [46]

    The Abstract and Introduction (page not provided) describe photoisomerization of 11-cis-retinal to all-trans-retinal and its regeneration through the retinoid cycle. The Introduction also describes high retinoid flux during intense light exposure, but does not establish that recycling back to 11-cis-retinal is quick. (LLM, conf=0.84)

    Experimental — accuracy not yet measured
  • RPE65 is an isomerohydrolase that catalyses hydrolysis of esters and isomerizes all-trans-retinol to 11-cis-retinol.

    “RPE65 is an isomerohydrolase that catalyses hydrolysis of esters and isomerizes all-trans-retinol to 11-cis-retinol [29,32,46].”

    From The Role of Vitamin A in Retinal Diseases (2022) · cites this paper as [46]

    Section 4.4.3 describes RPE65 as an isomerohydrolase that couples ester hydrolysis with retinoid isomerization. But Section 4.4.2 identifies retinyl esters—not free all-trans-retinol—as its natural substrates, so the claim misstates what RPE65 directly isomerizes. (LLM, conf=0.88)

    Experimental — accuracy not yet measured
  • When all-trans-retinal is released from opsin, it binds phosphatidylethanolamine to form N-retinylidene-phosphatidylethanolamine, which is transported by ABCA4 across the membrane to the cytoplasmic side of the photoreceptor.

    “When the all-trans-retinal is released from the opsin, on the luminal side of the photoreceptor membrane of rod discs and extracellular side in cones, it binds to the phosphatidylethanolamine to form N-retinylidene-phosphatidylethanolamine. The latter is transported by the ATP-binding cassette subfamily A member 4 transporter (ABCA4) across the membrane to the cytoplasmic side of the photoreceptor”

    From The Role of Vitamin A in Retinal Diseases (2022) · cites this paper as [46]

    The Introduction says that all-trans-retinal released from visual pigments can enter the disc lumen and is transferred toward the cytosol by ABCA4. Section 3.1 mentions conjugation of all-trans-retinal with phosphatidylethanolamine and says ABCA4 transports retinal or its metabolites, but the copy does not identify N-retinylidene-phosphatidylethanolamine as the transported molecule or establish the stated topology in cones. Page numbers were not available in the indexed passages. (LLM, conf=0.86)

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  • At the start of the visual cycle, all-trans-retinol enters the RPE through facilitated transport by STRA6 where it gets metabolized into a retinyl ester via the action of LRAT, which then converts to 11-cis retinol and subsequently 11-cis retinal through catalysis by RPE65 and RDH5.

    “At the start of the visual cycle, all- trans-retinol enters the RPE through facilitated transport by STRA6 where it gets metabolized into a retinyl ester via the action of LRAT, which then converts to 11-cis retinol and subsequently 11-cis retinal through catalysis by RPE65 and retinol dehydrogenase 5 (RDH5), respectively [53].”

    From Vitamin A Transporters in Visual Function: A Mini Review on Membrane Receptors for Dietary Vitamin A Uptake, Storage, and Transport to the Eye (2021) · cites this paper as [53]

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Authors
Kiser, P. D., Golczak, M., Maeda, A., & Palczewski, K.
Affiliations
Case Western Reserve University (US)
Corresponding author
  • Maeda, Akiko
  • Palczewski, Krzysztof
Venue
Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids
Publisher
Elsevier BV
Published
2012-01
Volume
1821
Issue
1
Pages
137-151
ISSN
1388-1981 (ISSN-L)
OpenAlex
W2000229924
Cited by
177
References
197
Citations by year
2026: 12 · 2025: 6 · 2024: 8 · 2023: 7 · 2022: 13 · 2021: 10 · 2020: 9 · 2019: 14 · 2018: 12 · 2017: 12 · 2016: 13 · 2015: 12 · 2014: 16 · 2013: 16 · 2012: 12
FWCI
1.39
Type
journal article
Language
en
Open access
Locations
  • Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids (publishedVersion)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (acceptedVersion)
  • PubMed Central (acceptedVersion)
Funders
  • National Institutes of Health (EY008061, P30 EY11373)
  • Foundation Fighting Blindness
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Retinal Development and Disorders
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Retinoids in leukemia and cellular processes
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Photoreceptor and optogenetics research
Keywords
retinoid cycle, visual cycle, all-trans-retinal, 11-cis-retinal regeneration, rhodopsin, phototransduction, retinal degeneration, acyltransferase, short-chain dehydrogenase/reductase, oxygenase, photoreceptors, retinal pigment epithelium, vitamin A metabolism
MeSH terms
Retinoid Isomerohydrolase, Acyltransferases, Alcohol Oxidoreductases, Animals, Carrier Proteins, Eye Proteins, Humans, Phospholipids, Retina, Retinal Diseases, Retinaldehyde, Retinoids, Rhodopsin, Vision, Ocular, cis-trans-Isomerases, Photoreceptor Cells, Vertebrate, Mice, Rats

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