Heterotrimer: presynaptic neurotoxin. Inhibits nerve-evoked twitch contractions but not responses to cholinergic agonists acetylcholine and carbachol and to depolarizing agonist KCl. Causes a fade in tetanic contractions. Displays a triphasic mode of action with depression, enhancement and blockade of neurotransmission. Does not display myotoxic activity such as changes in baseline muscle tension or inhibition of directly stimulated muscle twitches. All subunits are necessary for maximum toxicity. Monomer: Snake venom phospholipase A2 (PLA2) alpha chain that has enzymatic 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. Heterotrimer of alpha, beta and gamma chains, each related to PLA2. Expressed by the venom gland. Preincubation of this protein with monovalent antivenom or suramin prevents or delays toxicity, respectively. Antivenom fails to reverse neurotoxicity when applied at point of 90% neuromuscular blockade. Treatment of this protein with 4-bromophenacyl bromide drastically reduces enzymatic activity and toxicity, presumably by alkylating a His residue at the active site. Belongs to the phospholipase A2 family. Group I subfamily.