An investigation of the egg-white mucoproteins, ovomucoid and ovalbumin

Abstract

A semi-micro analytical procedure has been developed for the analysis of the carbohydrates present in mucoproteins. Ovomucoid was found to contain 2-amino-2-deoxy-D-glucose (12.3-12.8%), D-mannose (6.3%) and D-galactose (1.7%), whereas ovalbumin contained D-mannose (2.75%) and 2-amino-2-deoxy-D-glucose (1.34%). Specific cleavage of the protein-carbohydrate in ovomucoid and ovalbumin did not occur on treatment with picric acid, barium hydroxide or 0.01 N sulphuric acid. Various carbohydrate-enriched fractions were obtained by the action of barium hydroxide on ovomucoid. It is suggested that in this process the carbohydrate protion of the mucoprotein was also degraded from the reducing end with the loss of some mannose and amino sugar units and consequent enrichment of the galactose component. The partial acid hydrolysis of ovomucoid and ovalbumin was studied. Two disaccharides, a mannobiose and a D-mannosyl-2-amino-2-deoxy-D-glucose, were isolated in very small amounts from partial hydrolysates of ovomucoid. A glycopeptide was isolated from ovalbumin. The action of periodate on ovomucoid and ovalbumin was a two-stage reaction involving oxidation of both carbohydrate and protein. D- Galactose and D-mannose were shown to occur as non-reducing end groups in ovomucoid by using controlled hydrolysis, periodate oxidation and methyla-tion techniques. Methylation of ovomucoid and ovalbumin yielded products in which 2-amino-2-deoxy-D-glucose derivatives could not be detected. D-Mannose was found to occur as nonreducing end groups in the methylated carbohydrate of ovalbumin.