Metabolism of molecular species of phosphatidylethanolamine and phosphatidylcholine in rat hepatocytes during prolonged inhibition of phosphatidylethanolamine N-methyltransferase.

The metabolism of the molecular species of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) derived from [3H]ethanolamine has been studied in rat hepatocytes during prolonged inhibition of phosphatidylethanolamine-N-methyltransferase (PEMT) with 3-deazaadenosine (DZA). After an initial pulse of radioactivity for 1 h and a chase for up to 24 h in the presence or absence of DZA, the cells were harvested and the incorporation of label into the various molecular species of PE and PC was determined. Prolonged inhibition of PEMT did not affect the mol% distribution of either PE or PC molecular species. Thus, PE methylation is not required for the maintenance of cellular PE and PC molecular species composition. While the overall catabolism of PE was not affected by DZA treatment, inhibition of PEMT resulted in the selective degradation of 16:0-22:6-PE. The major catabolic products of PE in the hepatocytes and the medium were glycerophosphoethanolamine and ethanolamine-phosphate. PC, derived from PE, was remodeled at both the sn-1 and sn-2 positions and this process was not affected by the inhibition of PEMT. The major species being remodeled was 16:0-22:6-PC. The rapid turnover of 16:0-22:6-PE and PC species compared to other PE and PC species may be due to the presence of a 16:0-22:6 selective phospholipase.