| Summary: | In this study, the isolated guinea pig heart was pulse-labeled with a precursor of ethanolamine glycerophospholipid, and then chased with the non-radioactive compound for 0-8 h. Labeling with hexadecanol revealed that plasmanylethanolamine was the immediate precursor of plasmenylethanolamine, 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 labeling of phosphatidylethanolamine, and this ratio was maintained throughout the perfusion. The ratio of labeling is similar to the ratio of pool sizes of these ethanolamine glycerophospholipid in the heart, which implies that the CDP-ethanolamine pathway is also important for plasmenylethanolamine biosynthesis. The role of diradylglycerol in the synthesis of each ethanolamine glycerophospholipid was also investigated. The ratio of 1-alkenyl-2-acyl glycerol to total diradylglycerol content was 7% in the homogenate and 32% in the microsomes. However, ethanolamine 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 glycerol, but the formation of plasmenylethanolamine was not affected by 1,2-diacylglycerol. In addition, the inhibition of ethanolamine phosphotransferase by 1-alkyl-2-acyl glycerol appears to be an important mechanism for the coordination of plasmenylethanolamine biosynthesis via the desaturase reaction and the CDP-ethanolamine pathway.
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