Studies on the structure of carbohydrate moiety in ovoimucin.

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Ovomucin is a glycoprotein fraction of egg white characterized by high molecular weight and a contributor to the viscous property of egg white. A study was made on the electrophoretic analysis, fractionation and characterization of chalaza, and ovomucin from thick and thin albumen of the hen's egg. The chalaza and ovomucin were confirmed to be composed of three components which the molecular weights were estimated to be 150,000, 220,000 and 400,000 daltons, and named <alpha>1, <alpha>2 and <beta> respectively. They were fractionated into carbohydrate poor (<alpha>1 and <alpha>2 mixture) and rich (<beta>) components by gel filtration in the presence of SDS and 2-mercaptoethanol. The <beta>-component contains much higher concentrations of carbohydrates than <alpha>-component, except for mannose. The total content of carbohydrate amount to about 50 %, whereas that of <alpha>-component is about 11 %. The carbohydrate chain in <alpha>-ovomucin was considered asparagine-binding N-glycosidic type, whereas that in the <beta>-ovomucin is O-grycosidic type linked to serine or threonine.The <beta>-ovomucin was collected and hydrolyzed by proteinases. The carbohydrate chains linked to the glycopeptide were released by alkaline borohydrate treatment. Three acidic oligosaccharides were obtained by fractionation with DEAE-Sephadex ion exchange chromatography. Carbohydrate compositions were analyzed by gas chromatography, and followed by sequence analysis with direct MS of the permethylated oligosaccharides, GC-MS analysis of pertially methylated derivatives and by anomer analysis with ^<13>C-NMR. The chemical structures identified were Gal-<beta>-1-3-GalNAc-6-SO_3H, NANA-<alpha>-2-3Gal-<beta>-1-3-GalNAc-6-SO_3H, and NANA-<alpha>-2-3-Gal-<beta>-1-3-[NANA-<alpha>-2-3-]-GalNAc.