Acyltransferase activities in rat lung microsomes.

Some properties of acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyl-transferase in rat lung microsomes wed moiety of acyl-CoAs, quite different values were obtained on the Michaelis constant, the maximal velocity, and the activation energy. Moreover, the incorporation of fatty acid from an acyl-CoA was affected in a different manner by the addition of other acyl-CoAs. These results suggested that there are at least two different acyltransferases which are tentatively termed as follows: (1) palmitoyl-CoA: 1-acylglycerophosphorylcholine acyltransferase; and (2) arachidonoyl-CoA: 1-acylglycerophosphorylcholine acyltransferase. A low Km value, a low maximal velocity, and a low value of the activation energy were obtained for the former activity. The activity is readily inhibited by the addition of other acyl-CoAs and also at the higher concentration of palmitoyl-CoA itself. While a high Km value, a high maximal velocity, and a high value of the activation energy were obtained for the latter activity. The activity is not affected by the addition of palmitoyl-CoA or oleoyl-CoA and only slightly inhibited by linoleoyl-CoA, which indicates a high substrate specificity for polyenoyl-CoA especially for arachidonoyl-CoA. It seems that the present result, together with the previous findings obtained in slice experiments and in in vivo studies, do not support the idea that palmitoyl-CoA : 1-acylglycerophosphorylcholine acyltransferase participates in the main pathway for the formation of dipalmitoyllecithin in lung.