Lack of effect of RPE65 removal on the enzymatic processing of all-trans-retinol into 11-cis-retinol in vitro

RPE65 is a major membrane associated protein found in the vertebrate retina l pigment epithelium (RPE). Various studies have shown this protein to he e ssential for visual function, possibly at the level of the processing of re tinoids, The pigment epithelium is the anatomical site in which the visual chromophore 11-cis retinal is generated. The two critical RPE enzymes in th e isomerization pathway are lecithin retinol acyl transferase (LRAT) and is omerohydrolase, which processes all-trans-retinyl esters into 11-cis-retino l. Both enzymes are membrane bound. It is shown here that RPE65 can be larg ely extracted (90-95%) from RPE membranes by 1 M KCl by itself, or with add ed detergent CHAPS. The almost quantitative extraction of RPE65 from RPE me mbranes has little or no effect on in vitro LRAT and isomerohydrolase activ ities in quantitative enzymatic assays using RPE membranes, suggesting that RPE65 may not have an important role to play in the enzymatic processing o f all-trans-retinol into 11-cis-retinol in vitro. (C) 1998 Federation of Eu ropean Biochemical Societies.