An EDTA.Ca2+ complex inhibits the enzymatic activity but not the lethality of beta-bungarotoxin

An EDTA.Ca2+ complex inhibits the phospholipase A2 activity of the presynaptic neurotoxin beta-bungarotoxin without affecting its lethal potency. The EDTA.Ca2+ complex induces a conformational change in the enzymatic active site region of beta-BuTx, as indicated by the suppression of the 340 nm tryptophan fluorescence peak. Modification of the enzymatic site without loss of toxicity supports the presence of separate loci for the two activities.