Retinol dehydrogenase

The retinol that is delivered to the retinas of the eyes in this manner is accumulated by rod and cone cells. In the rods (which are the better characterized of the two cell types), retinol is oxidized by a specific retinol dehydrogenase to become 2iW-trans retinal and then converted to 11-eis retinal by reti-... 

FIGURE 18.36 The incorporation of retinal into the light-sensitive protein rhodopsin involves several steps. All- ram-retinol is oxidized by retinol dehydrogenase and then iso-merized to ll-cis-retinal, which forms a Schiff base linkage with opsin to form light-sensitive rhodopsin. 

A microsomal retinol dehydrogenase catalyzes the oxidation of CRBP-hound all-trans-retinol to retinaldehyde it also acts as a 3a-hydroxysteroid dehydrogenase. A similar enzyme catalyzes the oxidation of 9-cis- and 11-ds-retinol, but not all-trans-retinol again, it has 3a-hydroxysteroid dehydrogenase activity. In the eye, the major product of this enzyme is 11-cts-retinaldehyde, whereas in other tissues it is 9-cts-retinaldehyde, which is then oxidized to 9-cis-retinoic acid (Section 2.3.2.1 Chen et al., 2000 Duester, 2000, 2001 Gamble et al., 2000 NapoU, 2001). Although there is known to be an isomerase in the eye for the formation of 11-cts-retinaldehyde as a... 

Figure 2.3. Oxidative cleavage of j6-carotene by carotene dioxygenase (EC 1.14.99.36), and onward metabolism of retinaldehyde catalyzed by retinol dehydrogenase (EC 1.1.1.105) and retinaldehyde oxidase (EC 1.2.3.11).

Gamble MV, Mata NL, Tsin AT, Mertz IR, and Blaner WS (2000) Substrate specificities and 13-cis-retinoic acid inhibition of human, mouse and bovine ds-retinol dehydrogenases. Biochimica et Biophysica Acta 1476,3-8. 

Wang J, ChaiX, Eriksson U, and Napoli ]L (1999) Activity of human 11-cis-retinol dehydrogenase (Rdh5) with steroids and retinoids and expression of its mRNA in extraocular human tissue. Biochemical Journal 338, 23-7. 

S. Ishiguro, Y. Suzuki, M. Tamai, and K. Mizuno. Purification of retinol dehydrogenase from bovine retinal rod outer segments. J Biol Chem, 266, 15520-15524, 1991. 

K. Palczewski, S. JSger, J. Buczylko, R. Crouch, D. L. Bredberg, K. P. Hofmann, M. A. Asson-Batres, and J. C. Saari. Rod outer segment retinol dehydrogenase substrate specificity and role in phototransduction. Biochemistry, 33, 13741-13750, 1994. 

Simon, A., Heilman, U Wemstedt, C., and Eriksson, U. (1995). The retinal pigment epi-theLal-specific 11-crs retinol dehydrogenase belongs to the family of short chain alcohol dehydrogenases. /. Biol. Chem. 170, H07-JH2. 

Biochemical research has shown the importance of zinc metabolism in the retina (9). Zinc is found in high concentrations in the choroid, the retina, and especially the ganglion cells. Retinol dehydrogenase, a zinc-containing enzyme, interferes with the transformation of retinol (vitamin Ai), which is essential for color sensation and conal vision. Furthermore, zinc is involved in the biosynthesis of the specific transport of retinol from the liver to the effector cells. Ethambutol is a chelating... 

The fate of intracellular retinol is dependent on cell type. In the eye, trans-retinol can be esterified by LRAT or isomerized to ll-a>-ret-inol by a cell-specific isomerase (22). 11-cis-retinol is then oxidized to 11-cis-retinal by 11-cis-retinol dehydrogenase (22). 11-cis-retinal binds to opsin by forming a Schiff base with an opsin lysine residue and the resulting complex is known as rhodopsin (22). Rhodopsin is a member of the seven transmembrane family of proteins that serves as receptor for photons... 

Unlike many retinol dehydrogenases, the enzyme that catalyzes the conversion of retinol to anhydroretinol, retinol dehydratase, does not use CRBP-retinol as a substrate rather, it uses free retinol (49-51). However, the enzyme responsible for biosynthesis of 14-hydroxy-4,14-retro-retinol has not yet been isolated. 

Dalf6, D., N. Marques, and R. Albalat. 2007. Analysis of the Nadh-Dependent Retinaldehyde Reductase Activity of Amphioxus Retinol Dehydrogenase Enzymes Enhances Our Understanding of the Evolution of the Retinol Dehydrogenase Family. Febs J 274, no 14 3739-52. 

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