Phospholipid Methylation and Cellular Differentiation

Abstract

Phospholipid methylation is a reaction in which phosphatidylthanolamine (PtdEtn) and its alkyl and alkenyl analogues are converted to phosphatidylcholine (PtdCho) and its analogues with S-adenosyl methionine (S-AdoMet) as a methyl donor (Hirata, 1984). The highest specific activity of enzyme(s)(PtdEtn methyltransferase) that catalyzes this reaction is generally found in the plasma membranes of most tissues and cells, except for in the liver and lung where this enzyme activity appears to be highest in the microsomes. In the latter two tissues, PtdEtn methyltransferase(s) is supposed to be involved in the synthesis of biles and surfactants, respectively. We have previously proposed that at least two enzymes are involved in this reaction (Hirata and Axelrod, 1980). Recently, Makishima, et al.(1985) highly purified these enzymes from the plasma membranes of murine lymphocytes and characterized some properties of two different enzymes. The first enzyme mainly methylates PtdEtn and the other enzyme forms PtdCho by adding two more methyl groups to monomethyl-PtdEtn. These enzymes have different kinetic parameters with respects to affinities for S-AdoMet, metal dependency and optimal pH.