EFFECT OF COBALAMIN DEFICIENCY ON THE BIOSYNTHESIS OF PHOSPHATIDYLCHOLINE IN EUGLENA-GRACILIS

Euglena gracilis requires cobalamin (Cbl) as an essential growth facto r. Phosphatidylcholine (PC) synthesis was greatly reduced by Cbl defic iency. Rapid cell division occurred after Cbl was replenished, and PC was actively synthesized during the cell divisions. When the deficient cells were given methionine (a precursor for the choline moiety), act ive synthesis of PC occurred even without the Cbl supplement, although cell division was not induced. As methionine synthase in Euglena requ ires methylcobalamin as a coenzyme, decrease in methionine synthesis m ay account for reduced PC synthesis under Cbl-deficient conditions. Ph osphatidylethanolamine and phosphatidylserine synthesis were also supp ressed, commensurate with decrease of PC synthesis, under Cbl deficien cy, even though Cbl is not thought to participate in their synthesis. In contrast, a lot of triglyceride and wax ester accumulated in Cbl-de ficient cells. Moreover, Cbl depletion altered fatty acid composition, notably due to increased proportion of odd-numbered fatty acids.