Some aspects of methionine metabolism by Trypanosoma equiperdum, in vitro

Homogenates of Trypanosoma equiperdum contained approximately 2.3 g methionine per 100 g crude protein, as determined by two independent methods. Radioactivity derived from both l-methionine-14CH3 and d,l-methionine-14COOH was recovered in the acid-soluble, lipid, nucleic acid, and protein fractions of trypanosomes after their incubation in the presence of these labeled substrates. Methionine served as the source of methyl groups for the biosynthesis of choline, and possibly also for methylated purine and pyrimidine bases present in RNA and DNA.Most of the radioactivity derived from l-ethionine-ethyl-1-14C was recovered in the acid-soluble fraction of T. equiperdum incubated in the presence of this labeled substrate, but small amounts were also detected in the protein and nucleic acid fractions. l-Ethionine depressed the uptake of methionine by the trypanosomes to a greater extent than did the d-isomer.