Enzymic synthesis of 1-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamines by the CDP-ethanolamine: 1-radyl-2-acyl-sn-glycerol ethanolaminephosphotransferase from microsomal fraction of rat brain.

The incorporation of radioactivity from cytidine-5'-phosphate-[(32)P]phosphorylethanolamine into 1-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamines and 1,2-diacyl-sn-glycero-3-phosphorylethanolamines was stimulated more than fourfold by 1-alkyl-2-acyl-sn-glycerols and 1,2-diacyl-sn-glycerols, respectively, with an ethanolaminephosphotransferase (EC 2.7.8.1) present in the microsomal fraction from brains of mature rats. The K(m) values, 0.28 mm for CDP-ethanolamine and 1.9 mm for 1-alkyl-2-acyl-sn-glycerols, were similar to those obtained by other investigators with other 1-radyl-2-acyl-sn-glycerols. The formation of 1,2-diacyl-sn-glycero-3-phosphorylethanolamines from endogenous 1,2-diacyl-sn-glycerols was inhibited by 1-alkyl-2-acyl-sn-glycerols. These properties indicate that the ethanolaminephosphotransferase lacks specificity for the type of group at the 1-position of the lipid substrate. The synthesis of 1-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamines from 1-alkyl-2-acyl-sn-glycerols and CDP-ethanolamine by an enzyme from rat brain supports the inclusion of this reaction in the metabolic pathway for the synthesis of 1-alk-1'-enyl-2-acyl-sn-glycero-3-phosphorylethanolamines.