title: L-methionine catabolism in trichomonads.
abstract: Trichomonas vaginalis growing in complex medium produced volatile thiols at a rate of 0.7 nmol min-1 (mg protein)-1 and the parasite suspended in PBS with L-methionine excreted volatile thiols, including methanethiol, and alpha-keto acid. Cell-free extracts of the parasite also produced volatile thiols from L-methionine, at the rate of 5.4 nmol min-1 (mg protein)-1. Thiol production was not detectable with living cells or cell-free extracts of Tritrichomonas foetus, Trichomitus batrachorum or Pentatrichomonas hominis and homogenates of a range of trypanosomatids and mouse liver also failed to produce volatile thiols from L-methionine. Approximately equimolar concentrations of alpha-keto acid and volatile thiols were produced from L-methionine by cell-free extracts of Trichomonas vaginalis; the release of ammonia, however, was not detectable. The parasite enzyme catabolised a range of substrates and was inhibited by several compounds, including bithionol and DL-propargylglycine. Parasites grown in the presence of 10(-5) M DL-propargylglycine had no detectable L-methionine-catabolising enzyme activity. These findings indicate that T. vaginalis is significantly different from other trichomonads, a range of trypanosomatids and mouse liver in L-methionine catabolism, and that the parasite enzyme responsible for the breakdown of L-methionine in T. vaginalis appears to be similar in several ways to bacterial L-methionine-gamma-lyase (EC 4.4.1.11) and trichomonal homocysteine desulphurase (EC 4.4.1.2).
mesh_terms: D000818:Animals; D002474:Cell-Free System; D003470:Culture Media; D005740:Gases; D006863:Hydrogen-Ion Concentration; D008715:Methionine / Q000378:metabolism*; D013045:Species Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014244:Trichomonas / Q000201:enzymology / Q000378:metabolism*; D014246:Trichomonas vaginalis / Q000378:metabolism
chemical_list: D003470:Culture Media; D005740:Gases; D013438:Sulfhydryl Compounds; D008715:Methionine