Isolation of the Third Component of Complement (C3) from Carp Serum

The third component (C3) of carp complement was purified to homogeneity by a four-step purification procedure: 1) affinity chromatography on Blue-Cellulofine, 2) QAE-Sephadex A-50 chromatography, 3) gel filtration on Sepharose CL-6B, and 4) CM-Sephadex C-50 chromatography. Hemolytic activity of carp C3 was assayed using intermediate cells, EAC14, and hydrazine-treated carp serum. The final recovery of C3 activity was 17%. Carp C3 showed an electrophoretic mobility of B-globulin with a molecular weight of 194,000. The protein consisted of two carbohydrate-containing subunits of 120,000 (a-chain) and 74,000 (B-chain) which were linked by disulfide bonds. In agreement with mammalian C3, carp C3 was inactivated by nucleophilic attack by amines such as hydrazine, ammonia, hydroxylamine and methylamine, but it showed considerable resistance against chaotropic reagents such as KBr and KSCN. In addition, it was shown that carp C3 attached covalently to a zymosan particle as a result of the activation of the alternative complement pathway.