PURIFICATION AND CHARACTERIZATION OF EQUINE COMPLEMENT FACTOR-C3

A rapid method for purifying equine C3 which yields milligram quantiti es of pure C3 is described. Protein from equine plasma was selectively precipitated with polyethylene glycol, and the C3 was purified by ani onic and cationic exchange HPLC. The yield from this procedure was 12% . The purified C3 was composed of an alpha chain (118 kD) and a beta c hain (68 kD) linked by at least one disulfide bond, and it had an isoe lectric point of 4.7. Amino acid analysis indicated a strong conservat ion of amino acid usage between equine and human C3. The N-terminal se quences of the alpha and beta chains were homologous to human, mouse, and rat C3, and activation of C3 produced breakdown products similar i n molecular weight to C3b and iC3b of other species. Equine C3 appeare d to be functionally dependent upon a reactive thiolester as treatment of fresh equine serum with methylamine abrogated its hemolytic activi ty.