Selectivity and Regulation in the Phospholipase A2‐Mediated Attack on Cholinergic Synaptic Vesicles by β‐Bungarotoxin

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Abstract
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 .apprx. 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.