all-trans retinal
Summary
An oxidized metabolite of vitamin A essential for vision, functioning as the light-sensitive chromophore in rhodopsin. 11-cis-retinal binds opsin; light converts it to all-trans retinal, triggering phototransduction.
Detail
All-trans retinal is isomerized to 11-cis-retinal by RPE65 for binding to opsin (forming rhodopsin). Light causes photoisomerization back to all-trans, triggering the phototransduction cascade. RPE65 mutations cause Leber congenital amaurosis. Systemically, all-trans retinal can be oxidized to retinoic acid (ATRA), which regulates gene expression via RAR/RXR receptors. ATRA treats acute promyelocytic leukemia (APL/M3) by inducing blast differentiation. Vitamin A deficiency causes night blindness; excess causes hypervitaminosis A and teratogenicity.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Harrison's Principles of Internal Medicine
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