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. Author manuscript; available in PMC: 2006 Sep 5.
Published in final edited form as: Biochemistry. 2006 Apr 4;45(13):4210–4219. doi: 10.1021/bi052382x

Figure 1.

Figure 1

Chemistry of the retinoid cycle reactions in the vertebrate retina. The retinoid cycle reactions were reviewed recently (6). In the rod outer segments (ROS), light causes the isomerization of the rhodopsin chromophore, 11-cis-retinylidene, to all-trans-retinylidene, which is hydrolyzed and released from opsin. All-trans-retinal is then reduced in a reaction catalyzed by all-trans-retinal-specific RDH(s) including prRDH. All-trans-retinol diffuses to retinal pigment epithelium (RPE) where it is esterified by LRAT to fatty acid all-trans-retinyl esters. All-trans-retinyl esters or its derivative is isomerized to 11-cis-retinol in a reaction that involves an abundant RPE protein, termed RPE65. 11-cis-Retinol is then oxidized by 11-cis-RDH (RDH5, RDH11) and other dehydrogenases to 11-cis-retinal, completing the cycle. 11-cis-Retinal diffuses across the extracellular space, is taken up by the ROS, and recombines with opsin to regenerate rhodopsin. In aberrant reactions, all-trans-retinyl esters or its derivative is isomerized to 13-cis-retinol. 13-cis-Retinol can also be esterified by LRAT to form 13-cis-retinyl esters, stored in retinosomes.

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