DISTRIBUTION OF 11-CIS LRAT, 11-CIS RD AND 11-CIS REH IN BOVINE RETINAL-PIGMENT EPITHELIUM MEMBRANES

Our recent finding of the co-localization of 11-cis retinyl esters and 11-cis retinyl ester hydrolase (11-cis REH) activity in bovine retina l pigment epithelium (RPE) plasma membrane (PM) has led us to explore the possibility that the PM may provide 11-cis retinal for rhodopsin r egeneration. In the RPE, visual chromophore is synthesized via a membr ane associated 11-cis retinol dehydrogenase (11-cis RD). Accordingly, bovine RPE membranes enriched with either endoplasmic reticulum (ER) o r plasma membrane (PM) enzyme markers were prepared and assayed for vi sual cycle enzyme activities. Pronounced 11-cis RD activity was associ ated with both ER- and PM-enriched membrane fractions. In contrast, 11 -cis REH activity was mostly recovered in PM-enriched fractions while LRAT activity was found only in ER-enriched membranes. The finding tha t both 11-cis retinol and 11-cis retinal can be produced at the PM of the bovine RPE strongly suggests that 11-cis retinyl esters at this su bcellular locale serve as a precursor of visual chromophore for pigmen t regeneration. (C) 1998 Elsevier Science B.V. All rights reserved.