BIOSYNTHESIS OF PLASMENYLETHANOLAMINE K-1'-ENYL-2-ACYL-SN-GLYCERO-3-PHOSPHOETHANOLAMINE) IN THE GUINEA-PIG HEART

In this study, the isolated guinea pig heart was pulse-labeled with a precursor of ethanolamine glycerophospholipid, and then chased with th e non-radioactive compound for 0-8 h. Labeling with hexadecanol reveal ed that plasmanylethanolamine was the immediate precursor of plasmenyl ethanolamine, but a substantial portion of the label was also found in phosphatidylethanolamine. When ethanolamine was used as the precursor , the labeling of plasmenylethanolamine was between 50-65% of the labe ling of phosphatidylethanolamine, and this ratio was maintained throug hout the perfusion. The ratio of labeling is similar to the ratio of p ool sizes of these ethanolamine glycerophospholipid in the heart, whic h implies that the CDP-ethanolamine pathway is also important for plas menylethanolamine biosynthesis. The role of diradylglycerol in the syn thesis of each ethanolamine glycerophospholipid was also in investigat ed. The ratio of 1-alkenyl-2-acyl glycerol to total diradylglycerol co ntent was 7% in the homogenate and 32% in the microsomes. However, eth anolamine phosphotransferase displayed a distinct selectivity towards 1-alkenyl-2-acyl glycerol. Kinetic studies revealed that the synthesis of phosphatidylethanolamine was inhibited by 1-alkenyl-2-acyl glycero l, but the formation of plasmenylethanolamine was not affected by 1,2- diacylglycerol. In addition, the inhibition of ethanolamine phosphotra nsferase by 1-alkyl-2-acyl glycerol appears to be an important mechani sm for the coordination of plasmenylethanolamine biosynthesis via the desaturase reaction and the CDP-ethanolamine pathway.