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FORMATION AND LOSS OF CYSTEINE DURING ACID HYDROLYSIS OF PROTEINS. RÔLE OF TRYPTOPHAN

1947; Elsevier BV; Volume: 171; Issue: 2 Linguagem: Inglês

10.1016/s0021-9258(17)41068-4

1083-351X

Harold S. Olcott, H. Fraenkel‐Conrat,

Muscle metabolism and nutrition

CysteineBrand and Kassell (1) showed that an acid hydrolysate of chymotrypsinogen contained a considerable amount, of cysteine (1.3 per cent), although sulfhydryl groups could not be demonstrated in the intact protein, even after denaturation (1, 2).The meaning of this observation was not clear.Recently it was observed in this Laboratory that an acid hydrolysate of lysozyme, which also lacks detectable sulfhydryl groups, contained cysteine .The relatively high tryptophan contents of these proteins (6.0 and 8.0 per cent, respectively) suggested t,o us that this amino acid might be involved in the formation of cysteine.The experiments to be described confirmed the hypothesis t.hat tryptophan causes a reduction of cystine under the conditions used for the acid hydrolysis of proteins.In addition some further factors responsible for the amounts of cysteine determinable in protein hydrolysntes have been elucidated.For example, it has been shown that' there is slight but, detcct,able formation of cysteine when cystine alone is heated with acids.Such a reaction may account for the 0.6 per cent cysteine content, of an insulin hydrolysatc recorded by Brand (3).On the other hand, Halnwr and Sutting (4) have recently called attention to the disappearance of cysteine from acid hydrolysates of proteins.Cysteine, added either before or after acid hydrolysis, could not be quantitat.ivelyrecovered, even though oxidative destruction (by air) was minimized.It has nom been shown that the constituent responsible may be pyruvic acid, a substance that is present in prot.einhydrolysates from the decomposition of serine and possibly cystine peptides.The autoxidizability of cysteine in hydrochloric acid solution in the presence of copper ions has also been studied.