The Metabolism of Sulfur

The extent of the oxidation of the sulfur of the amino acid, cystine, by the animal organism has been the subject of frequent study (1, 2). It has been shown that the sulfur of cystine administered in moderate quantities is oxidized readily and excreted in bhe urine chiefly as sulfate sulfur. Variable recoveries of the sulfur of cystine when fed are frequently obtained, owing presumably to t,he ready decomposition of cystine by the intestinal microflora with the formaCon of hydrogen sulfide and mercaptans. It has also been observed that, if the a-amino group of cystine is blocked by some chemical group which prevents ready deamination in the organism (i.e. acetyl, benzoyl, etc.), the oxidation of the sulfur of the molecule is prevented to a very considerable extent (2-5). Our knowledge of the conditions for the oxidation of methionine, 6he second amino acid containing sulfur present in the protein molecule, is not extensive. Mueller (6), who first isolated methionine as a product of the hydrolysis of protein, observed in a limited series of experiments a ready oxidation of the sulfur of small quantities of methionine when fed to man. Pirie (7), after administering I-methionine equivalent to 320 mg. of sulfur to dogs, was able to recover 79 to 86 per cent of the sulfur fed as “extra” sulfur in the urine. A similar ready oxidation of the sulfur of dl-methionine by the dog has been not,ed by White and Lewis (8) and by Stekol and Schmidt (9).