Cysteine desulfhydration

Support for this enzymic desulfhydration came from the work of Metzler and Snell (72), who proposed a detailed chemical mechanism of desulfhydration in model experiments in the presence of pyridoxine and a metal ion. Similar enzyme models were proposed by others (73). The enzymic aspect of this reaction is not entirely satisfactory however, ce relatively little is known of the desulfhydrase enzyme, either derived from the liver (74) or from bacteria (75). In addition several pyridoxal phosphate-protein enzymes can catalyze cysteine desulfhydration (see Section IV). 

The enantiomers of this drug differ in their efficacy and activity, with (D)-penicilla-mine being the enantiomer required for pharmaceutical preparations. The (l)-enantiomer is toxic, and its absorption by the human body is more than the (D)-enantiomer. While both enantiomers of penicillamine are desulfhydrated by (r.)-cysteine desulfhydrase, only the (l)-isomer inhibits the action of this enzyme [2], The reported optical rotation values for (D)-penicillamine are ... 

D. Cavallini, B. Mondovi, C. De Marco and A. Scioscia Santoro. Inhibitory effect of mercaptoethanol and hypotaurine on the desulfhydration of cysteine by cystathionase. Arch. Biochem. Biophys., 1962, 96 456. 

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