Evidence for a lecithin-retinol acyltransferase activity in the rat small intestine.
Cellular retinol-binding protein, type II (CRBP (II] is an abundant protein of the mature enterocytes of the small intestine. It has been shown to direct retinol to an acyl-CoA-independent esterifying activity that utilizes an endogenous acyl donor (Ong, D.E., Kakkad, B., and MacDonald, P.N. (1987) J. Biol. Chem. 262, 2729-2736). Here we report that this activity in intestinal microsomes will catalyze the transfer of acyl moieties from exogenous phosphatidylcholine (PC) to retinol-CRBP(II) to produce retinyl esters. The microsomal activity displayed positional selectivity as only the sn-1-acyl moiety of PC was transferred to retinol-CRBP(II). The retinyl ester synthase was selective for PC substrates as acyl transfer from phosphatidylethanolamine, phosphatidic acid, or free fatty acid to retinol-CRBP(II) was not observed. Some formation of retinyl esters was observed with exogenous acyl-CoA, but the amount produced was considerably lower than ester formation from exogenous PC and could be shown to be due to a different enzyme activity. Inhibitor studies clearly distinguished between the enzyme activities responsible for the acyl-CoA-dependent esterification and the phosphatidylcholine-dependent esterification of retinol. The results provide strong evidence that retinol-CRBP(II) esterification in the intestine proceeds via a phosphatidylcholine-dependent transacylase mechanism similar to that established for the esterification of cholesterol by lecithin-cholesterol acyltransferase.
MacDonald
P N
PN
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Ong
D E
DE
D000214:Acyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D004951:Esterification; D007421:Intestine, Small / Q000201:enzymology*; D050356:Lipid Metabolism; D008297:Male; D008861:Microsomes / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D051142:Retinol O-Fatty-Acyltransferase; D012177:Retinol-Binding Proteins / Q000378:metabolism; D054840:Retinol-Binding Proteins, Cellular; D013379:Substrate Specificity; D014801:Vitamin A / Q000378:metabolism
D000214:Acyl Coenzyme A; D010713:Phosphatidylcholines; C518461:Rbp2 protein, rat; D012177:Retinol-Binding Proteins; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A; D000217:Acyltransferases; C056942:lecithin-retinol acyltransferase; D051142:Retinol O-Fatty-Acyltransferase