Self-association of bovine immunoglobulin G1

The self-association properties of bovine serum immunoglobulin G1 and colostral immunoglobulin G1 (IgG1) in 0.32 M-NaCl/0.01 M-Tris/HCl, pH 8.0, were investigated by analysing sedimentation data according to a monomer-dimer association model. The self-association was characterized by an equilibrium constant of 5.3 X 10(4) +/- 3.5 X 10(4) M-1 for serum IgG1 and 1.6 X 10(3) +/- 0.69 X 10(3) M-1 for colostral IgG1. The removal of the Fc portion of IgG1 by pepsin digestion abolished its property of self-aggregation. At high total protein concentrations of serum IgG1, low concentrations of the ostensible trimer species were observed. However, no self-aggregation was evident when 0.14 M-NaCl/0.01 M-sodium phosphate. pH 6.0, was used as a solvent, thus confirming results published previously [Tewari & Mukkur (1975) Immunochemistry 12, 925--930].