STUDIES ON THE METHYLATION OF ETHANOLAMINE PHOSPHATIDES BY LIVER PREPARATIONS

The phosphatidylmethyltransferase enzyme system of rat liver microsomes has been dispersed by treatment with deoxycholate and sonic oscillation. With the dispersed preparation, complete removal of endogenous phospholipid substrates could be achieved. The latter showed an absolute dependency on added N -monomethyl aminoethanol or N,N -dimethylaminoethanol phosphatides for methylation to lecithin. Kinetic study of the methylation reaction indicated that a single enzyme is involved which catalyzes the stepwise methylation of N -methylaminoethanol phosphatide to lecithin. Tests were made of the suggestion that phosphatidyl serine might be methylated prior to decarboxylation and, in this manner, might yield the first observed substrate, the monomethylethanolamine phosphatide. It was demonstrated that this reaction does not occur. The only decarboxylation product detected was ethanolamine phosphatide.