The Subcellular Distribution of Acyltransferases which Catalyze the Synthesis of Phosphoglycerides

The distribution of acyltransferase activities in rat liver homogenates is described in relation to that for five other enzymes, each known to belong to a certain subcellular particle. Five different transfer reactions were studied with 1‐acyl‐sn‐glycero‐3‐phosphorylcholine, 2‐acyl‐sn‐glycero‐3‐phosphorylcholine, 1‐acyl‐sn ‐glycero‐3‐phosphoylethanolamine, 1‐acyl‐sn‐glycero‐3‐phosphate and sn‐glycero‐3‐phosphate as substrates, and different acyl‐CoA esters served as donors of acyl groups. Glucose‐6‐phosphatase and the acyltransferase activities studied were distributed with similar relative specific activities among the subfractions. The results indicated that: a) Acyltransferases were located in the microsomal membranes. b) Nuclei and mitochondria did not have acyltransferase activity under the conditions used in these experiments, which were optimal for microsomal acyltransferases. c) Plasma membranes appeared to have only a small amount of acyltransferase activity in comparison to that in the microsomal particles. d) All acyltransferase activities tested showed similar patterns of distribution. e) Acyltransferase activities may be useful in the future as marker enzymes for microsomal particles from tissues which do not contain glucose‐6‐phosphatase, but do contain the acyltransferase within the microsomal membranes.