On the existence of an unidentified sulphur grouping in the protein molecule. Part I.—On the denaturation of proteins

Abstract

The hydrolysis of a protein substance which contains sulphur almost invariably results in the production of cystine among the decomposition products. This amino-acid almost certainly represents the actual form in which the bulk of the sulphur is combined in the molecule of most proteins. Cystine is, indeed, the only sulphur-body so far isolated which can be regarded with certainty as a primary dissociation product of protein. At the same time, there is a certain amount of evidence to suggest that in certain proteins—notably ovalbumin, and also casein—some of the sulphur is present in a form other than cystine. In the research about to be described this question was investigated mainly from two points of view:— (1) An examination was made of certain reactions given by egg white (and its products), attributable to sulphur groupings other than cystine. In the course of this work some light was thrown on the chemistry of denaturation.