An enzyme that catalyses the three-step methylation of phosphatidylethanolamine to phosphatidylcholine as well as the methylation of fatty acids and that uses S-adenosylmethionine as the methyl donor has been purified about 200-fold from rat liver. Irradiation of the purified enzyme with a short-wavelength u.v. light in the presence of [methyl-3H]8-azido-S-adenosylmethionine followed by electrophoresis results in the incorporation of radioactivity into a single protein band of about 25 kDa. It is concluded that a single catalytic subunit catalyses the conversion of phosphatidylethanolamine into phosphatidylcholine and fatty acid methylation.

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Epidermal growth factor produces a time-and dose-dependent activation of phospholipid methyltransferase activity in hepatocytes isolated from juvenile and mature hepatectomized rats. This treatment however has no effect with hepatocytes isolated from mature or laparotomized rats. Dansylcadaverine (50cM), an inhibitor of receptor-mediated internali~tion of epidermal growth factor, has no effect on basal phospholipid methyltransferase but inhibits the stimulation of this enzyme by epidermal growth factor.These results indicate a possible role of phospholipid methylation during liver proliferation.~hospholipid methyIation Epidermal growth factor Hepatocyte Liver regeneration

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