Selectivity and regulation in the phospholipase A2-mediated attack on cholinergic synaptic vesicles by beta-bungarotoxin.

The total fatty acid composition of purified Torpedo californica electric organ synaptic vesicles was determined by GLC analysis of methyl esters. Limit amounts of fatty acids released by high concentrations of either beta-bungarotoxin (beta-BuTx) or Naja naja venom phospholipase A2 (PLA2) acting in deoxycholate are reported. The time and enzyme concentration dependence for beta-BuTx- and PLA2-induced release of fatty acids from intact synaptic vesicles indicate that PLA2 is 100- to 1,000-fold more active. The Ca2+ dependence for beta-BuTx-induced release of fatty acids also was determined. ATP inhibits beta-BuTx- but not PLA2-induced release of fatty acids from vesicles in a manner that can not be ascribed only to chelation of the required Ca2+. ATP, other nucleotides, and adenosine have complex effects on beta-BuTx-induced release of fatty acids from egg yolk phosphatidylcholine dispersed in deoxycholate. The results suggest that beta-BuTx-mediated hydrolysis of the cholinergic synaptic vesicle membrane is approximately 10- to 100-fold more effective at causing uncoupling of vesicles than is PLA2 and that the enzymatic activity of beta-BuTx is subject to regulation by nucleotide-like factors.