Isolation and Characterization of a 4 S α2-β1-Glycoprotein of Normal Human Plasma

Abstract

Abstract A 4 S α2-β1-glycoprotein was isolated from Cohn Fraction VI of pooled normal human plasma by chromatography on diethylaminoethyl- and carboxymethylcellulose, Sephadex A-50, and hydroxylapatite columns and by filtration through Sephadex G-100. The final preparation appeared homogeneous after starch gel and disc electrophoresis at pH 5.0 and 8.6. Physicochemical and chemical characterization of this plasma globulin revealed the following properties: molecular weight, approximately 60,000; sedimentation coefficient, 4.1 S; diffusion constant, 5.9 x 10-7 cm2·sec-1; frictional ratio, 1.50; axial ratio, approximately 8; electrophoretic mobility at pH 8.6, 3.9 x 10-5 cm2·sec-1·volt-1; isoelectric point at pH 4.0; and isoionic point at pH 4.9. The optical rotatory dispersion curve of the native protein revealed a trough with a maximum at 218 mµ. In 50% 2-chloroethanol, this maximum was shifted to approximately 232 mµ, whereas in 5 m urea the trough was noted at 211 mµ. The carbohydrate moiety accounted for approximately 30% of the total weight and consisted of neutral hexoses (galactose and mannose), glucosamine, sialic acid, and fucose. This glycoprotein contains one polypeptide chain as judged from terminal amino acid analyses (1 mole of carboxyl-terminal serine and 1 mole of amino-terminal arginine). The content of the 4 S α2-β1-glycoprotein in pooled normal human plasma was estimated to be approximately 20 mg/100 liters.