Beta-bungarotoxins are presynaptic neurotoxins of the venom. The B chain is homologous to venom basic protease inhibitors but has no protease inhibitor activity and blocks voltage-gated potassium channels (Kv) (By similarity). Heterodimer; disulfide-linked. The A chains have phospholipase A2 activity and the B chains show homology with the basic protease inhibitors (By similarity). Expressed by the venom gland. Belongs to the venom Kunitz-type family.