Studies of the microsomal acylation of l-glycerol-3-phosphate I. The specificity of the rat brain enzyme

The specificity of acyl-CoA : L-glycerol-J-phosphate acyltransferase from rat brain microsomes for the fatty acid of the acyl-CoA was determined. Acyl-CoA's containing saturated fatty acids from 15 to 18 carbons were good substrates, while ones containing 14 and 19 carbon chains were used efficiently but at a lower rate. The Michaelis constant for r_-glycerol-x-phosphate was 0.4 mM and was not dependent on the acyl-CoA concentration : however, the kinetics of the acyl-CoA's was complicated by the micellar nature of these substrates. The product appeared to be phosphatidic acid. Acyl-CoA's could be replaced by MgATP, CoA and a fatty acid although the addition of a fatty acid was not strictly necessary since considerable endogenous fatty acids are present in microsomes. On the basis of these studies, it is concluded that the observed fatty acid composition and the preferential distribution of fatty acids in neutral fats and in phospholipids do not result from the substrate specificity of this enzyme.