Purification and Characterization of the 2 S γ2-Globulin of Normal Human Plasma

Abstract

Abstract A 2 S γ2-globulin was isolated from Cohn Fraction VI of pooled normal human plasma by chromatography on diethylaminoethyl and carboxymethyl cellulose columns and filtration through Sephadex G-100. Its plasma level was estimated to be approximately 0.1 mg/100 ml. Physicochemical and chemical characterization of this globulin revealed the following properties: molecular weight, 14,000; sedimentation coefficient, 1.9 S; diffusion constant, 13.5 x 10-7 cm2 sec-1; frictional ratio, 1.03; axial ratio, approximately 2; electrophoretic mobility at pH 8.6 in Γ/2 = 0.1 diethylbarbiturate buffer, -1.5 x 10-5 cm2 sec-1 volt-1; and isoelectric and isoionic points at pH 5.9 and pH 9.0, respectively. The optical rotatory dispersion suggested the presence of a β conformation and the probable absence of α-helical structures. This protein, which was shown to be free of carbohydrates, probably possesses one polypeptide chain, as judged by the terminal amino acid analyses (1 mole of carboxyl-terminal valine and 1 mole of amino-terminal tyrosine). The amino acid composition of this globulin differed significantly from those of Bence-Jones proteins and of the L chain of the 7 S γ-globulin.