All-trans to 11-cis retinol isomerization in nuclear membrane fraction from bovine retinal pigment epithelium.
Isomerization of all-trans to 11-cis retinol has been studied in a membrane preparation from the nuclear fraction of bovine retinal pigment epithelium. When the nuclear membrane preparation deprived of endogenous retinoids is incubated with 4.5 microM all-trans-retinol, the mean value calculated for the isomerase activity is 1.32 nmol 11-cis retinol formed hr-1 mg protein-1. Simultaneous formation of all-trans and 11-cis retinyl esters is also observed in the nuclear preparation. When assayed under the same experimental condition, RPE 150,000 g post-nuclear sediment shows about 70% of the isomerase activity found in the nuclear membrane fraction. Treatment of the nuclear membrane fraction with 0.5% (w/v) CHAPS produces a 200,000-g supernatant retaining 80% of the total isomerase activity and leads to a modest purification of the enzyme activity. Apparent values for Km and Vmax of the solubilized enzyme are 1.6 microM and 2.5 nmol 11-cis retinol formed h-1 mg protein-1, respectively. Bovine serum albumin and beta-lactoglobulin effectively stimulate the isomerization reaction. The mechanism underlying this activating effect remains unclarified at present. Some hypotheses are discussed.
Livrea
M A
MA
Institute of Biological Chemistry, University of Palermo, Italy.
Tesoriere
L
L
Bongiorno
A
A
D000818:Animals; D002417:Cattle; D002467:Cell Nucleus / Q000648:ultrastructure; D002793:Cholic Acids / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003902:Detergents / Q000494:pharmacology; D007535:Isomerases / Q000378:metabolism; D007536:Isomerism; D009685:Nuclear Envelope / Q000201:enzymology; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D012995:Solubility / Q000187:drug effects; D014801:Vitamin A / Q000737:chemistry*; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D002793:Cholic Acids; D003902:Detergents; D007535:Isomerases; D014801:Vitamin A; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate