Beta bungarotoxin is a presynaptic neurotoxin. The A chain has phospholipase activity. PLA2 catalyzes the calcium-dependent hydrolysis of the 2-acyl groups in 3-sn-phosphoglycerides. a 1,2-diacyl-sn-glycero-3-phosphocholine + H2O = a 1-acyl-sn-glycero-3-phosphocholine + a fatty acid + H(+) Binds 1 Ca(2+) ion. 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 phospholipase A2 family. Group I subfamily. D49 sub-subfamily.