Snake venom phospholipase A2 (PLA2) that inhibits neuromuscular transmission by blocking acetylcholine release from the nerve termini. 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 chains have phospholipase A2 activity and the B chains show homology with the basic protease inhibitors. The A1 chain is found in beta-1 and beta-2 bungarotoxins. Expressed by the venom gland. LD(50) is 0.019 mg/kg by intraperitoneal injection (beta-1 bungarotoxin) and LD(50) is 0.028 mg/kg (beta-2 bungarotoxin). Belongs to the phospholipase A2 family. Group I subfamily. D49 sub-subfamily.