Isolation and characterization of a serine-threonine-rich galactoglycoprotein from normal human plasma.
A serine-threonine-rich galactoglycoprotein was isolated in homogeneous form from pooled normal human plasma. After precipitation of the major portion of the plasma proteins by Cohn's low temperature-low salt-ethanol procedure, the proteins and glycoproteins remaining in the supernatant solution of Cohn Fraction V were concentrated with the aid of DEAE-cellulose. Fractional elution from this ion exchange resin yielded a crude preparation of the galactoglycoprotein which was purified subsequently by gel filtration through Sephadex G-100. Homogeneity of the protein was established by several criteria of purity including disc polyacrylamide gel electrophoresis and COOH-terminal amino acid analysis. The major physicochemical constants of the macromolecule including its molecular weight of 81,000 were measured. The chemical composition of this protein was found to be unusual: the total carbohydrate moiety accounts for 76% of its weight and consists of 23% sialic acid, 23% total neutral sugar, including 20% galactose, 1% fucose, and almost equal amounts of GalNAc and GlcNAc totalling 27%. The polypeptide moiety accounting for 26% of the weight of the glycoprotein distinguishes itself by a high content of serine and threonine.
D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D002942:Circular Dichroism; D005690:Galactose / Q000032:analysis*; D006023:Glycoproteins / Q000097:blood* / Q000302:isolation & purification; D006801:Humans; D008970:Molecular Weight; D011487:Protein Conformation; D012694:Serine / Q000032:analysis*; D012995:Solubility; D013912:Threonine / Q000032:analysis*
D000596:Amino Acids; D002241:Carbohydrates; D006023:Glycoproteins; D013912:Threonine; D012694:Serine; D005690:Galactose