Dye-ligand affinity purification of human complement factor B and beta 2 glycoprotein I.

The rapid purification of human factor B using dye-ligand chromatography is described. The 50% ammonium sulphate supernatant of fresh human serum is equilibrated in pH 7.4, 25 mM Tris buffer containing 0.5 mM CaCl2 and 0.5 mM MgCl2, with 25 mM sodium caprylate and chromatographed on Cibacron Blue F3GA-agarose. Caprylic acid binds to the fatty acid binding site of albumin, preventing it from binding to the resin which thus retains a high capacity for binding factor B. Factor B together with the homologous protein beta 2I are eluted from the column by a linear gradient of KCl. Subsequent NaCl gradient FPLC on Hiload S-Sepharose, equilibrated in 10 mM potassium phosphate, 5 mM EDTA, pH 7.0, provides both factor B and beta 2I in homogeneous form.