Abstract
We have isolated and partially characterized a 32-kDa membrane-associated protein (p32), which forms a complex with p63, an abundant membrane protein in bovine retinal pigment epithelium. The sequence of a cDNA clone for p32 revealed an open reading frame encoding 318 amino acid residues. Several hydrophobic regions could be identified, suggesting that p32 is an integral membrane protein. A search of data bases identified p32 as a member of the superfamily of short chain alcohol dehydrogenases. Transcripts for p32 were specifically expressed in retinal pigment epithelium. Overexpression of p32 in Cos cells produced a membrane-bound stereospecific 11-cis retinol dehydrogenase, active in the presence of NAD+ as cofactor but not in the presence of NADP. We propose that p32 is the stereospecific 11-cis retinol dehydrogenase, which catalyzes the final step in the biosynthesis of 11-cis retinaldehyde, the universal chromophore of visual pigments.
Highlights
Under normal physiological conditions, most cells obtain alltrans retinol as their major source of retinoid
All-trans retinol, which has been generated in the photoreceptor cells after light exposure ofthe visual pigments, is taken up through the apical plasma membrane for regeneration of 11-cis retinaldehyde
Available data show that membrane receptors for retinol-binding protein are expressed by RPE cells (8, 9), and retinol uptake by the apical plasma membrane is presumably mediated by the interstitial retinol-binding protein located in the space between the RPE
Summary
Vol 270, No., Issue of January 20, pp. 1107-1112, 1995 Printed in U.S.A. The Retinal Pigment Epithelial-specific II-cis Retinol Dehydrogenase Belongs to the Family of Short Chain Alcohol Dehydrogenases*. The major physiologically active derivatives of retinol, retinoic acid in nonocular tissues (1), and 11-cis retinaldehyde for ocular tissues (2) are generated by specific cellular mechanisms. None of these mechanisms have been fully defined at the molecular level, and several of the enzymes involved have only been characterized as enzymatic activities (3-6). All-trans retinol, which has been generated in the photoreceptor cells after light exposure ofthe visual pigments, is taken up through the apical plasma membrane for regeneration of 11-cis retinaldehyde. At present, it is not known whether similar mechanisms are used. Enzymatic analyses showed that p32 is a stereospecific H-cis retinol dehydrogenase
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
