Kappa-flavitoxin: isolation of a new neuronal nicotinic receptor antagonist that is structurally related to kappa-bungarotoxin

A peptide, termed kappa-flavitoxin ( k-flavitoxin), has been purified from the venom of the red-headed krait, Bungarus flaviceps, by low- and high-pressure liquid chromatography. k-Flavitoxin has apI 8.8 and an apparent molecular weight on sodium dodecyl-sulfate-polyacrylamide gel electrophoresis of 6500 Da. k-Flavitoxin is a inhibitor of nicotinic transmission in autonomic ganglia, producing a complete and long-lasting blockade at doses as low as 50 nM. Intracellular recordings reveal a selective blockade of neuronal nicotinic receptors by the toxin, with no effects on other active or passive properties of neuronal membranes. k-Flavitoxin shares a number of pharmacological and biochemical properties with k-bungarotoxin, purified from the venom of Bungarus multicinctus. The two peptides exhibit considerable homology in their amino acid sequences. Radiolabeled k-flavitoxin binds to a nicotinic site in ciliary ganglia previously identified by k-bungarotoxin, which appears to be associated with the neuronal nicotinic receptor. This site is not recognized by α-bungarotoxin, which also does not block nicotinic transmission in this ganglion.