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 does CVF/Bb). Heterotrimer of alpha, beta and gamma chains; disulfide-linked. Is active with factor B in the presence of factor D. 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). Interestingly, a peptide (from position 1111 to position 1125) coming from the pre-pro-protein has been identified by MS/MS, suggesting a longer gamma-chain in AVF-1 than in CVF. Belongs to the venom complement C3 homolog family.