The Metabolism of Sulfur

In previous studies (1, 2, 3) one of us (L.) has reported experiments which are concerned with the oxidation of sulfur in the cystine molecule. It was demonstrated that if deamination of cystine be prevented by “blocking” the amino group (as in phenyluraminocystine (1) or dibenzoylcystine (3) ), the sulfur of the molecule was not oxidized normally and was excreted in the urine in large part in the unoxidized sulfur fraction. However, if normal oxidation of the sulfur was prevented in this way, it was shown that the cystine was converted to cysteine and a considerable amount of the cystine derivative administered appeared in the urine as a derivative of cysteine (2,3). Recently Sherwin and his collaborators (4, 5) have reported similar results which in general confirm our earlier experiments. They also showed that if a derivative of cysteine with the amino group protected from deamination was fed to a rabbit, the cysteine was in part converted to cystine. Our own results and those of Sherwin are in accord with the current theory of the ready reversibility of the reaction cysteine + cystine. Many other investigations which are related to the oxidation of various types of sulfur linkages in organic combination have been reported. Inasmuch as this present study is concerned only with the oxidation of mercapto or sulfide sulfur of the type similar to that naturally occurring in the protein molecule, a complete