Biochemical characterization of the retinoid isomerase system of the eye

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Publication Type Journal Article
School or College School of Medicine
Department Ophthalmology
Creator Bernstein, Paul S.
Other Author Law, W C; Rando, R R
Title Biochemical characterization of the retinoid isomerase system of the eye
Date 1987
Description We have previously shown that membranes from the retinal pigment epithelium can transform added all-trans-retinol into a mixture of 11-cis-retinoids, demonstrating the "missing reaction" in the visual cycle for the first time (Bernstein, P. S., Law, W. C., and Rando, R. R. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1849-1853). In this article, this isomerase activity is further characterized. Double-label experiments with [15-3H]- and [15-14C]all-trans-retinol as the substrate show that the tritium label is retained in the 11-cis-retinol and 11-cis-retinyl palmitate products. This requires that isomerization occur at the alcohol level of oxidation. All-trans-retinyl esters, such as the palmitate, acetate, butyrate, and hexanoate esters, are not directly transformed into their 11-cis counterparts by the membranes. The data are consistent with the presence of an all-trans-retinol isomerase enzyme system or enzyme complex, which produces 11-cis-retinol. Other isomeric retinols were tested for substrate activity. Neither 9-cis-retinol(al) nor 13-cis-retinol were processed by the isomerase. Since the membranes containing the isomerase possess other retinol metabolizing activities, such as retinyl ester synthetase and dehydrogenase activities, further purification was attempted. Appreciable quantities of all detergents tested led to the disappearance of isomerase activity, and high salt or EDTA did not dissociate isomerase activity from the membranes. However, extensive sonication of the membranes did produce a 100,000 x g supernatant fraction of light membranes depleted of other all-trans-retinol processing activities. The isomerase activity in these membranes was saturable with all-trans-retinol, as required for a biologically significant process, and showed a Vmax of 5 pmol/h/mg of protein, a KM of 0.8 microM, and a pH optimum of 8. The isomerase was destroyed by proteinase K, by phospholipase C, by heating, or by ethanol at concentrations greater than 1%. The addition of high energy compounds, such as MgATP, MgGTP, or palmitoyl-CoA, did not appear to stimulate isomerase activity in the 100,000 x g supernatant.
Type Text
Publisher American Society for Biochemistry and Molecular Biology (ASBMB)
Volume 262
Issue 35
First Page 16848
Last Page 16857
Subject Hydrogen-Ion Concentration
Subject MESH Eye; cis-trans-Isomerases; Phospholipase C; Retinaldehyde
Language eng
Bibliographic Citation Bernstein PS, Law WC, Rando RR. (1987). Biochemical characterization of the retinoid isomerase system of the eye. J Biol Chem, 262(35), 16848-57
Rights Management (c)American Society for Biochemistry and Molecular Biology (ASBMB)
Format Medium application/pdf
Identifier ir-main,1750
ARK ark:/87278/s6m623vc
Setname ir_uspace
Date Created 2012-06-13
Date Modified 2021-05-06
ID 706575
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