Complement-activating protein in snake venom. It is a structural and functional analog of complement component C3b, the activated form of C3. It binds factor B (CFB), which is subsequently cleaved by factor D (CFD) to form the bimolecular complex AVF/Bb. AVF/Bb is a C3 convertase that cleaves complement component C3, but not C5 (as do CVF/Bb) (By similarity). Heterotrimer of alpha, beta and gamma chains; disulfide-linked. Is active with factor B in the presence of factor D (By similarity). Expressed by the venom gland. First processed by the removal of 4 Arg residues by furin-type protease, forming two chains, alpha and gamma/beta precursor, linked by a disulfide bond. This mature AVF is composed of three chains: alpha, gamma and beta (By similarity). Is expressed in small quantities. Belongs to the venom complement C3 homolog family. Lacks the typical Cys at position 1000 required for the thioester bond formation.