The reactions of the sulfur-containing amino acids with phosphoric and sulfuric acids

Abstract

Both cystine and cysteine react very differently toward 6.0 M phosphoric and sulfuric acids. With phosphoric acid, extensive decomposi tion occurs; with sulfuric acid, very little. Cystine, in phosphoric acid at 100 °C. produces hydrogen sulfide, free sulfur, cysteic acid, ammonia, alanine, serine, and pyruvic acid. Cysteine produces a similar series but with marked quantitative differences. Cystine, in sulfuric acid, is merely racemized. Methionine is largely demethylated by sulfuric acid under these conditions. It is practically inert toward phosphoric acid. The behavior of hair toward phosphoric and sulfuric acids is similar to that of cystine but is modified by reactions of other hydrolytic products.