The expression and activity of cystathionine-γ-lyase and 3-mercaptopyruvate sulfurtransferase in human neoplastic cell lines
Changes of the specific activity of 3-mercaptopyruvate sulfurtransferase (MPST), rhodanese and cystathionase in Ehrlich ascites tumor cells (EATC) and tumor-bearing mouse liver after intraperitoneal administration of thiazolidine derivatives, L-cysteine, D,L-methionine, thiocystine or thiosulfate were estimated. Thiazolidine derivatives used were: thiazolidine-4-carboxylic acid (CF), 2-methyl-thiazolidine-2,4-dicarboxylic acid (CP) and 2-methyl-thiazolidine-4-carboxylic acid (CA). In the liver, the activity of MPST was significantly increased by all the studied compounds, whereas the activity of rhodanese was by CF and thiocystine and that of cystathionase was by the administration of cysteine and CP. Un the other hand, cysteine lowered the rhodanese activity and the activity of cystathionase was decreased by the administration of methionine and thiocystine. Activities of MPST and rhodanese were even lower in EATC than those in the liver of tumor-bearing mouse and the activity of cystathionase in EATC was not be detected. The thiazolidine derivatives significantly increased the level of MPST activity in EATC, but decreased the rhodanese activity. Thiosulfate also increased the activity of MPST to a lesser degree, but cysteine, methionine and thiocystine gave little change in the activity. The rhodanese activity in EATC was slightly increased only by thiocystine. These findings suggest that the sulfur metabolism in the tumor-bearing mouse liver is different from that in the normal mouse liver, and that sulfur compounds are minimally metabolized to sulfane sulfur, a labile sulfur, in EATC.