Further Studies on Metabolism of Sulfur Compounds in Cystinuria.*

∗Aided by Grant No. 302 from the Committee on Scientific Research of the American Medical Association. Some recent experiments,2 on sulfur metabolism have been confirmed on another case of cystinuria (16-year-old female from a cystinuric family). Cystine (6.4 gm.), administered orally was almost completely (98%) oxidized to inorganic sulfate and did not increase urinary cystine excretion. Cysteine (3.5 gm.), on the other hand, was largely excreted as extra cystine (45%) and only a part of it was oxidized (38% of the extra sulfur). Methionine (dl, 6 gm.) was also largely excreted as extra cystine (40%) and partly (35%) as undetermined neutral sulfur, while only a small amount (25% of the extra sulfur) was oxidized. A preliminary experiment with 2.5 gm. of homocystine indicates that in cystinuria this amino acid is oxidized (92% of the extra sulfur) and does not give rise to extra cystine in the urine. The implications of this finding will be discussed upon completion of confirmatory experiments now in progress on another patient. The cystine in the urine of this patient, as determined by our modification of the Sullivan method, increased with the ageing of the specimen in agreement with earlier observations.