Mechanism of the sulfur lability in the alkali degradation of wool protein

Abstract

It is the purpose of this paper to describe the behavior of sulfur in wool under conditions which are very different from those ordinarily used in studies on sulfur lability and to point out a probable mechanism by which sulfur is split from wool during alkali treatment. The data indicate tha t the primary process in the alkali cleavage of the disulfide linkage consist s in a hydrolytic rupture of the disulfide group with the formation of a sulfh ydryl compound and a sulfenic acid. The sulfenic acid is ext remely reactive a nd u nstable in alkaline solution and immediately loses hydrogen sulfide and forms a n a ld eh yde. The results of the investigation indica t e that the existence of labile sulfur in prot eins is not an indication that the bulk of the sulfur is present in more than one form.

Nature of the reaction of wool with alkali

“…For example, his explanation calls for the production of sulfhydryl and aldehyde groups, whereas tests for each of these groups on hydrolysates of the alkali-treated wool were definitely negative. As pointed out earlier [2], there existed the possibility that recombination between the aldehydic and sulfhydryl groups may have occurred under the conditions of the hydrolysis. However, it was subsequently shown [6] that few if any free sulfhydryl groups are present in the alkali-treated wool even prior to hydrolysis.…”

“…While it is recognized that the values obtained by isolation methods are always low, nevertheless it should be possible to form larger amounts of this amino acid in the alkali-treated material if the reaction proceeds as suggested. On the basis of earlier work [2], it appears that sodium sulfide, one of the products of the reaction of wool with allmli, could interfere with the formation of lanthionine in either of two ways. It might compete with cysteine in the reaction with dehydroalanine (eq 3), or it could split unreacted disulfide linlmges and thus lower the amount of dehydroalanine that could be produced.…”

“…In earlier investigations [1 , 2,3]2 it was shown that such degradation is closely associated with the lability toward alkalies of the disulfide groups in the cystine of the wool. A study of the course of the degradation revealed that during the early stages, a rapid spli tting off of a portion of the sulfur occurred, the amount of sulfur being lost closely approaching 50 percent of the original totall21.…”

“…The sulfenic acid, being extremely reactive and unstable in alkaline solution, immediately loses H 2S to form an aldehyde as follows: (2) Another possibility given consideration at that time was that proposed by Nicolet [5], who postulated that the removal of sulfur from cystine by alkalies takes place as an elimination of hydrogen sulfide from an intermediate enolized form according to the following equation:…”

“…The question as to the fate of the l'esidualnoncystine sulfur in the treated wool arises. Earlier [2] it was suggested that a stable thiocompound was formed. Thus, for example, if the view of Sch6berl were correct, a thioacetal could be formed.…”