FIGURE 6.

Schematic of retinoid metabolic pathways. The schematic illustrates the role of RDH10 in the biosynthesis of all-trans-retinoic acid for development and differentiation and in the biosynthesis of 11-cis-retinaldehyde for vision. The 11-cis-retinol dehydrogenase activity of RDH10 is marked with a star to indicate that this activity has not yet been demonstrated in vivo. REH, retinyl ester hydrolase; RPE65, isomerohydrolase; ALDH, aldehyde dehydrogenase. Other abbreviations are as described in the legend to Fig. 2. Note that the NAD⁺-dependent RDH10 and RoDH4 function in the oxidative direction, whereas the NADP⁺-dependent RDH12 functions in the reductive direction. Lecithin:retinol acyltransferase (LRAT) appears to utilize all-trans-retinol bound to CRBPI, whereas the oxidoreductases exclusively recognize the unbound all-trans-retinol as a substrate.