Purification and Characterization of the 2 S y,-Globulin of Normal Human Plasma*

A 2 S y,-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/lOO 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’ cm2 se@; frictional ratio, 1.03; axial ratio, approximately 2 ; electrophoretic mobility at pH 8.6 in I’/2 = 0.1 diethylbarbiturate buffer, -1.5 X lo+ cm* set+ volt-l; and isoelectric and isoionic points at pH 5.9 and pH 9.0, respectively. The optical rotatory dispersion suggested the presence of a /I conformation and the probable absence of (Yhelical 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 y-globulin.