Complement Component 4c (C4c)

C4b was cleaved by C3bINA in the presence of C4b-binding protein and C4d and C4c isolated. The radioactive label and therefore the reactive thiol group were located to C4d. C4c was reduced and alkylated and the two alpha'-chain fragments of C4c were separated. The molecular weights, amino acid analyses and carbohydrate content of the three alpha'-chain fragments were determined. C4d has a mol.wt. of 44500 and a carbohydrate content of 6%. The two alpha'-chain fragments of C4c have mol.wts. of 25000 and 12000 and carbohydrate contents of 10 and 22% respectively. The N-terminal amino acid sequences of C4d, the alpha 3 and the alpha 4 fragments were determined for 18, 24 and 11 residues respectively and, by comparison with the N-terminal sequence of the C4b alpha'-chain, the 25000-mol.wt. fragment was shown to be derived from the N-terminal part of the alpha'-chain.C-Terminal analyses were done on the alpha'-chain and its three fragments.