The Decomposition of Cysteine in Aqueous Solution*

In a recent study (1) it was shown that cystine could be decomposed by boiling distilled water with the formation of cysteine, hydrogen sulfide, and elementary sulfur. The decomposition of cysteine under similar conditions should aid in a clearer explanation of the mechanisms involved in the breakdown of these two amino acids. The action of alkaline reagents on cysteine and its derivatives has been studied by Andrews (2), Clarke (3), Gortner (4), Nicolet (5), Schoberl (6), and their collaborators. Treatment of cysteine with 2 M sodium hydroxide for 5 hours at 100’ resulted in 3 to 5 per cent deamination (2), while boiling with 1 M sodium hydroxide for the same period produced about 7 per cent deamination (3). These results were confirmed by Thor and Gortner (4) who stated that cysteine was definitely more stable toward boiling 4 M sodium hydroxide than was cystine. On the other hand it was recently observed (6) that no loss in nitrogen resulted when cysteine was heated to 98-99” in 1 M sodium hydroxide for 2 hours. The results of experiments in which cysteine was decomposed under the conditions previously established for the decomposition of cystine are presented in this paper.