Cysteine metabolism in the cestodeHymenolepis diminuta

Abstract

SUMMARYThe major pathways for cysteine catabolism inHymenolepis diminutahave been investigated. The parasite has an active cystathionine-β-synthase and, as in other tissues, this enzyme has a wide substrate specificity. However, the enzyme fromH. diminutadiffers significantly from the mammalian enzyme in showing a high serine sulphydrase activity and a high serine lyase activity. There was only low γ-cystathionase activity inH. diminutaand again the enzyme showed a range of substrate specificities. Cysteine aminotransferase activity was readily demonstrated in the tapeworm, but there was no evidence for 3-mercaptopyruvate sulphotransferase activity. An oxidative pathway for cysteine catabolism inH. diminutawas shown by the presence of cysteine dioxygenase and cysteine sulphinate transaminase. The properties of the helminth cysteine dioxygenase were very similar to those of rat liver.H. diminutawas able to reduce cystine to cysteine via a glutathione-cysteine transhydrogenase system.