Beta-bungarotoxin is a presynaptic neurotoxin of the venom. The B chain is homologous to venom basic protease inhibitors but has no protease inhibitor activity and is non-toxic (By similarity). Heterodimer; disulfide-linked. The A chain has phospholipase A2 activity and the B chain shows homology with the basic protease inhibitors (By similarity). Expressed by the venom gland. Belongs to the venom Kunitz-type family.