Inhibition of rat liver CDPethanolamine: 1,2-diacylglycerol ethanolamine-phosphotransferase activity by ATP and pantothenic acid derivatives

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Abstract
The properties of rat liver microsomal CDPethanolamine:1,2-diacylglycerol ethanolaminephosphotransferase (ethanolaminephosphotransferase; EC 2.7.8.1) are studied with respect to metal ion and substrate concentration. The enzyme requires Mg2+ (20 mM) or Mn2+ (1 mM) for optimum activity. Mn2+ are better activators of ethanolaminephosphotransferase activity than are Mg2+. Ca (1 mM) inhibits the Mg2+-activated ethanolaminephosphotransferase by 86% and the Mn2+-activated enzyme by 57%. The Km for CDPethanolamine is 2.4 and 0.7 .times. 10-4 M, in the presence of Mg2+ or Mn2+, respectively. ATP plus CoA or ATP plus pantetheine significantly inhibit the Mn2+-activated ethanolaminephosphotransferase, while the Mg2+-activated enzyme is inhibited by ATP plus pantetheine and slightly stimulated by ATP plus CoA. In the presence of either metal ion, ATP itself inhibits enzyme activity, while CoA or pantetheine when added alone have no effect. Evidence is presented indicating that the inhibition of ethanolaminephosphotransferase activity by ATP plus CoA or ATP plus pantetheine is not due to the formation of acyl-CoA or acyl-S-pantetheine esters. At the present time the true mechanism of inhibition is unknown. The cellular levels of ATP, CoA, pantetheine, Mg2+, Mn2+ and Ca2+ may all play a role in the regulation of phosphatidylethanolamine biosynthesis.