beta-Bungarotoxin, a pre-synaptic toxin with enzymatic activity.

beta-Bungarotoxin, a pre-synaptic neurotoxin isolated from the venom of the snake Bungarus multicinctus, has been shown to modify release of neurotransmitter at the neuromuscular junction. In this communication, we demonstrate that beta-bungarotoxin is a potent phospholipase A2 (phosphatide 2-acyl hydrolase, EC 3.1.1.4), comparable in activity with purified phospholipase enzymes from Naja naja and Vipera russellii. The phospholipase activity of beta-bungarotoxin requires calcium and is stimulated by deoxycholate. When strontium replaces calcium, no phospholipase activity is detected. Since neuromuscular transmission is not blocked when calcium is replaced by strontium, it was possible to examine the effects of the toxin on neuromuscular transmission in the presence of strontium. Under these conditions, when the phospholipase activity should be inhibited, the toxin has little or no effect on neuromuscular transmission. If beta-bungarotoxin owes its toxicity in part to its enzymatic activity, then it must be placed in a different class from those toxins which produce their effect by binding passively to an appropriate receptor.