Factors Which Influence the Stability of Tryptophan during the Hydrolysis of Proteins in Alkaline Solution*

The stability of tryptophan, when heated in alkaline solution under conditions suitable for the hydrolysis of proteins, has been studied by a number of investigators. In general, the older reports indicate that a somewhat irregular loss of tryptophan usually occurs. With regard to the causes of this loss, the report of Lugg (l), showing that the addition of stannite resulted in partial stabilization of tryptophan, is of particular significance as it indicates that the destructive reaction is one of oxidation. The results of Brand and Kassell (2) are in agreement with this conception. The production of indole from proteins as well as from pure tryptophan by heating these substances in alkaline solutions was studied by Herzfeld (3). When relatively large amounts of copper sulfat,e were added, 60 per cent of the tryptophan was converted to indole. This suggests that even traces of copper or other heavy metals might influence the stability of tryptophan. The wide-spread adoption of microbiological methods for amino acid analysis focuses new attention on the best method for the hydrolysis of proteins and especially of foodstuffs for tryptophan determination. Greene and Black (4) found autoclaving with 5 r; Ba(OH)z for 5 hours a satisfactory procedure. Stokes et al. (5) adopted the procedure of autoclaving for 10 hours with 5 N NaOH. Hauschildt et al. (6) also used sodium hydroxide for hydrolysis and apparently considered it satisfactory. In contrast with these reports, Wooley and Sebrell (7) found tryptophan to be relatively unstable when autoclaved with NaOH. The report of Greenhut et al. (8) indicated the same thing. These differences in results presumably were due to differences in material or conditions. It is the purpose of this report to present data showing some of the factors which can alter the stability of tryptophan and to present a procedure by which tryptophan can be completely stabilized during the