title: Specific inactivation of isomerohydrolase activity by 11-cis-retinoids.
abstract: The endergonic trans-->cis isomerization of retinoids is an essential element in rhodopsin regeneration in vertebrates. All-trans-retinyl esters, which are generated by lecithin retinol acyltransferase (LRAT), are on the isomerization pathway. The critical isomerohydrolase activity, which catalyzes the trans-->cis isomerization/hydrolysis reaction of all-trans-retinyl esters, remains to be identified. It is demonstrated here that 11-cis-retinyl bromoacetate (cRBA) is a potent and specific inactivator of the bovine retinyl pigment epithelial (RPE) isomerohydrolase activity, with a measured K(I)=0.19 microM and a pseudo-first-order rate of inactivation k(inh)=1.83 x 10(-3) s(-1). This demonstrates that the isomerization is indeed enzyme-mediated. This inactivator should facilitate the identification and study of isomerohydrolase, or at least an essential component of it. Labeling of crude RPE membranes with 3H-cRBA reveals the presence of several labeled bands that may be isomerohydrolase candidates.
mesh_terms: D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D002417:Cattle; D004224:Diterpenes / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004952:Esters / Q000737:chemistry / Q000378:metabolism; D006867:Hydrolases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007536:Isomerism; D015394:Molecular Structure; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000201:enzymology; D000084562:Retinyl Esters; D014801:Vitamin A / Q000737:chemistry / Q000378:metabolism; D019745:cis-trans-Isomerases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D004224:Diterpenes; D004791:Enzyme Inhibitors; D004952:Esters; D000084562:Retinyl Esters; D014801:Vitamin A; C034831:retinyl bromoacetate; D000217:Acyltransferases; C056942:lecithin-retinol acyltransferase; D006867:Hydrolases; D019745:cis-trans-Isomerases