CATABOLISM OF CYSTEINE, CYSTINE, CYSTEINESULFINATE, AND OTC BY ISOLATED-PERFUSED RAT HINDQUARTER

The metabolism of cysteine and related compounds was investigated in the isolated perfused hindquarter of the rat. An erythrocyte-based perfusion medium was used; use of a perfluorochemical emulsion, FC-43, resulted in apparent chemical oxidation of cysteine, whereas bovine erythrocytes did not appear to contribute significantly to the metabolism of cysteine. Rat skeletal muscle perfused with L-[S-35]cysteine, L-[S-35]cystine, L-[S-35]cysteinesulfinate, or L-2-oxo-[S-35]thiazolidine-4-carboxylate (OTC) for 2 h produced [S-35]sulfate and [S-35]taurine. In all cases, the partitioning of cysteine or cysteinesulfinate between metabolism to taurine and sulfate was similar, suggesting that cysteine metabolism in hindquarter may occur via formation and catabolism of cysteinesulfinate by either cysteinesulfinate decarboxylase or aspartate (cysteine-sulfinate) aminotransferase. However, the activity of cysteine dioxygenase was extremely low, suggesting that the conversion of cysteine to cysteinesulfinate may have been non-enzymatic.