Binding characteristics of the bungarotoxin fraction II-S1 to rat brain membranes

Bungarotoxin fraction II-S1 (designated BGT II-S1), isolated from the venom of Bungarus multicinctus, appears to affect nicotinic transmission in rat sympathetic ganglia through its phospholipase activity. On the other hand, the present investigation suggests that other modes of interaction of this toxin with nervous tissue may also exist as, in a rat brain membrane preparation, binding of this toxin to a specific binding site can be demonstrated. In a buffer containing calcium, binding of [125I]BGT II-S1 saturated with a Bmax of approximately 16 fmol/mg protein and a Kd of 5 nM. This site did not appear to be directly linked to the nicotinic acetylcholine recognition site as the binding was not displaced by nicotinic agents; however, alpha-bungarotoxin, which interacts with a nicotinic-like site in neural tissue, did affect the binding and, conversely, BGT II-S1 inhibited the binding of [125I]alpha-bungarotoxin.