Studies on Cryoprecipitation: IV. ENZYMIC FRAGMENTS OF A HUMAN CRYOGLOBULIN

Abstract

Abstract Studies on the enzymic fragmentation of a single component 6.5 S human cryoglobulin (γ1:λ, Gm factor 4), obtained from a patient suffering from idiopathic cryoglobulinemia, were undertaken to gain a better understanding of the mechanism of temperature-dependent gel formation and its relation to the gross structure of the cryoglobulin molecule. Proteolytic scission of cryoglobulin by papain produced Fab monomers and Fc dimers of apparent molecular weights of 44,600 and 48,900, respectively. Papain fragments, individually or collectively, did not form gel. The Fab (papain) fragments, however, exhibited a dimer-monomer equilibrium dependent on the hydrogen ion concentration of the milieu. Treatment of the cryoglobulin with pepsin produced two F(ab)2 fragments, F1(ab)2 and F2(ab)2, and one Fc fragment of apparent molecular weight of 105,600, 93,000, and 40,500, respectively. The disulfide-linked pepsin fragments formed gel in neutral and alkaline buffers at 3°. An increase in the molecular size of the F(ab)2 fragments and alkaline pH produced greater gel formation. Sedimentation velocity analysis with F1(ab)2 fragment under varying conditions of temperature and pH revealed the formation of a dimer as a major polymer component and a trimer as a minor one. Carbohydrate analyses showed the presence of 10 residues of hexoses (galactose and mannose), 2 residues of fucose, 6 residues of glucosamine, and 2 residues of sialic acid.