Carbohydrates in protein. 5. Procedures for the isolation of glycopeptides from hen's-egg albumin and their oxidation by periodate

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Abstract
The rate and extent of enzymic hydrolysis of egg albumin was studied for three systems: (a) pepsin followed by trypsin and chymotrypsin together, (b) Pronase-P and (c) papain followed by Pronase-P. Techniques involving the use of Sephadex G-25 are described for the isolation of glycopeptides from these enzymic digests. Yields of glycopeptide by methods (b) and (c) are very high. The amino acid constituents in these purified glycopeptides were compared. These were used to point out the changes in specificity of the enzyme depending on whether the whole protein or the glycopeptide is the substrate. A method suggested by Bogdanov et al. (1961) for obtaining glycopeptide with aspartic acid as the only amino acid constituent has been confirmed and the usefulness of the procedure was demonstrated. The carbohydrate-aspartic acid complex obtained gave a brown colour when treated on paper with ninhydrin under the conditions described. The significance of this is discussed. Quantitative studies of periodate uptake by a purified glycopeptide preparation were made. The formic acid liberated and the quantities of mannose and glucosamine oxidized were also measured. These studies make it probable that the carbohydrate is either linear or has a maximum of one branch point.