Characterization of an 11,000-dalton beta-bungarotoxin: binding and enzyme activity on rat brain synaptosomal membranes.

The binding and phospholipase A2 activity of an 11,000-dalton β-bungarotoxin, isolated from Bungarus multicinctus venom, have been characterized using rat brain subcellular fractions as substrates. 1z51-labeled p-bungarotoxin binds rapidly (k = 0.14 min-l and 0.1 1 min-l), saturably (V max = 130.1 -+- 5.0 fmoles/mg and 128.2 ±7.1 fmoles/mg), and with high affinity (apparent KCI = 0.8 ± 0.1 nM and 0.7 ± 0.1 nM) to rat brain mitochondria and synaptosomal membranes, respectively, but not to myelin. The binding to synaptosomal membranes is inhibited by divalent cations and by pretreatment with trypsin. The binding results suggest that the toxin binds to specific protein receptor sites on presynaptic membranes. The 1 1,000-dalton toxin rapidly hydrolyzes synaptosomal membrane phospholipids to lysophosphatides and manifests relative substrate specificity in the order phosphatidyl ethanolamine > phosphatidyl choline > phosphatidyl serine. These results indicate that the 1 1,000-dalton p-bungarotoxin is a phospho...