Transamination and transsulphuration of L-cysteine in Ehrlich ascites tumor cells and mouse liver. The nonenzymatic reaction of L-cysteine with pyruvate.

1. The activity of cysteine aminotransferase (CAT), 3-mercaptopyruvate sulfurtransferase (MPST) and rhodanese is much lower in Ehrlich ascites tumor cells (EATC) than in mouse liver. 2. Contrary to mouse liver homogenate, no synthesis of sulphane sulphur-containing compounds from L-cysteine is observed in EATC homogenate. 3. 2-Methyl-thiazolidine-2,4-dicarboxylic acid (CP), 2-methyl-thiazolidine-4-carboxylic acid (CA) and thiazolidine-4-carboxylic acid (CF) can be used as sources of low molecular-weight thiol compounds both in EATC and mouse liver homogenate. 4. Pyruvate formed from phosphoenolpyruvate (PEP) in EATC homogenates reacts with L-cysteine (L-CYS) to CP.