S-adenosylmethionine and transmethylation reactions in trichomonads.

S-Adenosylmethionine (SAM) levels in trichomonads, a range of trypanosomatids and mouse liver were measured using HPLC techniques. The concentrations were found to be similar in each with the exception of Herpetomonas muscarum ingenoplastis, which contained approximately ten-fold more. Living trichomonads were found to incorporate exogenous L-methionine into intracellular SAM and its methyl carbon was also detected in lipids and nucleic acids, presumably through its involvement in transmethylation reactions. Norleucine and cycloleucine inhibited L-methionine uptake and incorporation into living Trichomonas vaginalis. Both the rates of incorporation of exogenous L-methionine into intracellular SAM and its involvement in transmethylation reactions were greater for Trichomonas vaginalis than for Tritrichomonas foetus. The results suggest that Trichomonas vaginalis and other trichomonads contain enzymes equivalent to SAM synthetase (EC 2.5.1.6) and SAM-dependent methyltransferases (EC 2.1.1).