Cystathionine β-synthase and γ-cystathionase in helminths

Abstract

The activities of γ-cystathionase and cystathionine β-synthase were investigated in a range of gastrointestinal, free-living and entomophagous nematodes. Although nermatode γ-cystathionase used the same range of substrates as the mammalian hepatic enzyme, its activity was extremely low and there were significant interspecies variations with respect to the relative order of active substrates. Like the mammalian liver enzyme, nematode cystathionine β-synthase showed activity in the directions of both cystathionine synthesis and the for-ward and reverse “l-serine sulphhydrase” reactions. However, the most important feature of the survey was the widespread ability of nematode cystathionine β-synthase to catalyse the non-mammalian “activatedl-serine sulphhydrase” reaction (l-cysteine+R-SH→cysteine thioether+H₂S). Additional survey work revealed that the ability to catalyse the activatedl-serine sulphhydrase reaction was almost universal amongst nematodes. Activatedl-serine sulphhydrase activity was also demonstrated in the acanthocephalanPomphorhynchus laevis but was absent from cestodes and digeneans.