Purification and biochemical characterization of a mouse submandibular sialomucin

A sialomucin from the mouse submandibular gland was isolated and purified by a protocol involving Sephacryl S-200 chromatography, acidic dialysis, and preparative, poly(acrylamide)-gel electrophoresis. The mucus glycoprotein was judged to be free from contaminants by analytical and sodium dodecyl sulfate-poly(acrylamide)-gel electrophoresis, isoelectric focusing, immunoelectrophoresis, and immunodiffusion when made visible by Stains-all, periodic acid-Schiff reagent, and Coomassie Blue. The carbohydrate portion constituted 81% of the weight of the mucus glycoprotein, and was composed of 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose, sialic acid, D-galactose, and D-mannose. Neither L-fucose nor sulfate was detected. The aliphatic amino acids constituted 60% of the protein core. The sialomucin has an apparent mol. wt. of 140,000 by sodium dodecyl sulfate-gel electrophoresis, and a pI of 2.77-3.63 by isoelectric focusing.