The Metabolism of Sulfur

The relation of the cystine of the diet to the growth and composition of the hair of young white rats has been established (l-3). In the absence of adequate amounts of dietary cystine, optimal growth of the hair was not observed and the cystine and sulfur contents of the hair were lower than those of rats maintained on diets supplying ample amounts of cystine. The ingestion of cystine in quantity in excess of the normal physiological requirements, however, failed to result in the production of a “superkeratinized” hair (3). Methionine has been shown to function similarly to cystine, both for purposes of growth in rats fed a diet inadequate in its content of cystine (4, 5) and for the detoxication of monobromobenzene (668). The administration of either cystine or methionine to bile fistula dogs was followed by an augmented excretion of taurocholic acid in the bile (9). When methionine was fed to cystinuric individuals, an increased excretion of cystine by the kidneys was observed (10, 11). The evidence available thus indicates a close relationship in metabolism between the two chief sulfur-containing amino acids of the protein molecule. Rose (12) has suggested that methionine may replace cystine of the diet entirely for purposes of growth of the young white rat, but that there is a minimal dietary requirement for methionine and that cystine cannot be substituted effectively for all of the dietary methionine. In view of these facts, it has seemed important t,o determine