2—THE COMPETITIVE ADDITION REACTION OF DEHYDROALANINE RESIDUES FORMED DURING THE ALKALINE DEGRADATION OF WOOL CYSTINE

Abstract

An investigation is described in which the effect of a thiol-reducing agent, thioglycollic acid, on wool in borate and ammonia solutions was ascertained in relation to the competition of thiols and amines for combination with dehydroalanine residues. Thioglycollate was found to decrease the amounts of products formed by amino-group addition to dehydroalanine residues at pH 12 and to eliminate them completely at pH 10. It is also shown that, at certain concentrations of thioglycollate, the degradation of cystine to dehydroalanine residues is greatly increased to give maximum lanthionine formation, but above this critical concentration thioglycollic acid competes successfully with the thiol group of cysteine to give S-carboxymethylcysteine rather than lanthionine. Differences between alkaline solutions of borates and ammonia with thioglycollate present are ascribed to the differences in reduction of cystine to cysteine; the blocking of free thiol groups is used to observe any difference in the amount of sulphur-containing products found after hydrolysis of the wool keratin.