The carbohydrate units of asialo-ovomucoid: their heterogeneity and enzymic degradation.
An ovomucoid variant free from sialic acid has been prepared in a pure state by ion-exchange chromatography on DEAE-cellulose. The purified glycoprotein contained 10-11 residues of mannose, 2-3 residues of galactose, and 21 residues of 2-acetamido-2-deoxyglucose. Glycopeptides have been prepared by exhaustive digestion with Pronase followed by ion-exchange chromatography on Dowex 50 (X2) resin. Three fractions were obtained, all with similar contents of mannose and hexosamine but with various contents of galactose. The sugar-aspartic acid ratios indicated that all of the fractions were heterogeneous, the major fraction having mannose-galactose-hexosamine-aspartic acid ratios of 2.6:0.5:5.8:1.0. Cleavage of asialo-ovomucoid with cyanogen bromide and proteolytic digestion of the isolated fragments gave two heterogeneous glycopeptide fractions of similar composition. Both asialo-ovomucoid and the principal glycopeptide fraction were degraded with beta-D-galactosidase, alpha-D-mannosidase, and beta-N-acetylglucosaminidase singly and in sequence. Removal of much of the carbohydrate from asialo-ovomucoid had no appreciable effect on its anti-tryptic activity. By sequential degradation of the glycopeptide, a pentasaccharide core alpha-D-Man-[alpha-D-Man]-beta-D-Man-beta-D-GlcNAc-beta-D-GlcNAc-Asn was obtained. Other structural features revealed by enzymic degradation are discussed.
D000818:Animals; D001212:Asialoglycoproteins; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002417:Cattle; D004527:Egg Proteins; D014644:Genetic Variation; D006020:Glycopeptides / Q000032:analysis; D006026:Glycoside Hydrolases; D008970:Molecular Weight; D009844:Oligosaccharides / Q000032:analysis*; D010059:Ovomucin / Q000031:analogs & derivatives; D012794:Sialic Acids / Q000032:analysis; D014357:Trypsin / Q000378:metabolism
D001212:Asialoglycoproteins; D004527:Egg Proteins; D006020:Glycopeptides; D009844:Oligosaccharides; D012794:Sialic Acids; C037370:asialoovomucoid; D010059:Ovomucin; D006026:Glycoside Hydrolases; D014357:Trypsin