Characterization of glycoproteins isolated from porcine zonae pellucidae

Two glycoproteins, tentatively designated as PZ-alpha and PZ-beta, have been isolated and purified to homogeneity from porcine zonae pellucidae by a simple purification procedure producing a high yield. The procedure included the dissolution of the zona material in 0.1 M sodium borate buffer pH 10.0, Sephadex G-100 column chromatography and preparative SDS-polyacrylamide gel electrophoresis. The purified glycoproteins gave a single band on polyacrylamide gel and had molecular weights of 60 000 (PZ-alpha) and 96 000 (PZ-beta). Glutamic acid was detected as the NH2-terminal residue in both glycoproteins, using the dansyl chloride method. Though their amino acid compositions were similar, their carbohydrate contents were slightly different (PZ-alpha: 24.9%; PZ-beta; 19.6%), but these components contained the same types of monosaccharides: fucose, mannose, galactose, NAcGlc and sialic acid. The antigenic properties of the two glycoproteins were indistinguishable by immunodiffusion tests. The PZ-beta could be converted in part to smaller molecular weight components, though not to PZ-alpha, by treatment with beta-mercaptoethanol. Thus clear differences between PZ-alpha and PZ-beta could not be detected by chemical or immunological analyses except for the difference in the behaviour on SDS-polyacrylamide gel electrophoresis.