In vivo isomerization of all-trans- to 11-cis-retinoids in the eye occurs at the alcohol oxidation state
The vertebrate biochemical pathway for regeneration of visual pigments in the living eye after bleaching is largely uncharacterized. Since isomerization of an all-trans-retinoid to an 11-cis-retinoid could conceivably occur via the aldehyde, alcohol, or ester forms of vitamin A, it is important to determine the oxidation state of the retinoid that is isomerized in vivo. To address this problem, light-adapted rats and frogs were injected intraperitoneally with a mixture of (15-/sup 3/H)-all-trans-retinol and (15-/sup 14/C)-all-trans-retinol. After 4 or 24 h of dark adaptation, labeled retinoids in the animal's eyes were analyzed. All rats had the expected 50% loss of /sup 3/H label (relative to /sup 14/C) in 11-cis-retinal, a loss of /sup 3/H that must occur when (15-/sup 3/H)retinol is oxidized to retinal. 11-cis-Retinyl esters in the rats' eyes at 4 h retained 67% of the /sup 3/H label, and this could be increased to 81% when the rats were pretreated with 4-methylpyrazole, an alcohol dehydrogenase inhibitor known to inhibit dark adaptation. This result demonstrates that retinoid isomerization occurs at the alcohol oxidation state in the rat eye. Had it occurred at the aldehyde oxidation state, at least 50% of the /sup 3/H in the 11-cis-retinyl esters would have been lost. The importance of this isomerization pathway is emphasized by the observation that dark-adapting rats whose alcohol dehydrogenase(s) had been inhibited by 4-methylpyrazole had increased amounts of 11-cis-retinyl ester in their eyes relative to control rat eyes, a result that is understandable only if retinoids are isomerized in vivo at the alcohol oxidation state.
- Research Organization:
- Harvard Medical School, Boston, MA
- OSTI ID:
- 7035567
- Journal Information:
- Biochemistry; (United States), Vol. 21
- Country of Publication:
- United States
- Language:
- English
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RETINOIC ACID
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BIOLOGICAL PATHWAYS
CARBON 14 COMPOUNDS
EPITHELIUM
FROGS
IN VIVO
RATS
REDOX REACTIONS
RETINA
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VITAMIN A
AMPHIBIANS
ANIMAL TISSUES
ANIMALS
AQUATIC ORGANISMS
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CHEMICAL REACTIONS
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EYES
FACE
HEAD
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
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VERTEBRATES
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550201* - Biochemistry- Tracer Techniques