Abstract
Human C 4 binding protein (C 4 bp), which is a macromolecular weight (Mr 450, 000-590, 000) cofactor of C 3 b/C 4 b inactivator (I), is composed of 6 or 8 disulfide-linked polypeptide chains of Mr 75, 000. Chymotrypsin cleaved C 4 bp into two major fragments; a large fragment of Mr 160, 000, which contained carbohydrate chains and was composed of disulfide-linked polypeptide chains of Mr 25, 000, and a small fragment of Mr 48, 000, which was a single polypeptide chain and had the cofactor activity of C 4 bp. These results suggest that chymotrypsin liberates a functional domain-containing Mr 48, 000 fragment from each subunit chain of C4bp and yields a core fragment derived from a disulfide-knot domain connecting each subunit chain of C4bp.
