Methionine, Cysteine, Cystine, and Taurine Interrelationships in Human Plasma

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Abstract
Methionine-, cysteine-, cystine-, and taurine-tolerance studies were carried out in healthy human adult subjects to investigate the interrelationships among these S-containing compounds in the plasma. A concomitant increase in methionine and cysteine was found during the methionine test, while cystine concentrations remained constant. In contrast, when cystine was the test amino acid, increased amounts of cysteine appeared in the plasma; and when cysteine was ingested, a concomitant increase in cystine occurred. There was a rapid and sustained increase in plasma taurine concentration during the taurine-tolerance test. Ingestion of test loads of the S-containing amino acids had little or no effect on the amounts of the other amino acids in plasma.