Jiang_1986_Toxicon_24_713

A postsynaptic acting short chain alpha-toxin, B.f. III, was isolated from venom of the banded krait (Bungarus fasciatus) using ion-exchange chromatography. The toxin, a basic protein (pI = 10) has an apparent molecular weight of 6,500 as determined by SDS-polyacrylamide gel electrophoresis. It shares immunological determinants with alpha-bungarotoxin, as it cross-reacted with antibodies raised in rabbits against alpha-bungarotoxin. B.f. III inhibits binding of 125I-alpha-bungarotoxin to cultured chick myotubes with an IC50 of 3 X 10(-10) M. The rate of association with chick myotube nAChR was 3 times faster than that of alpha-bungarotoxin, and binding was slowly reversible. The toxin is a less potent antagonist than alpha-bungarotoxin; in ion flux experiments, measuring influx of 86Rb in chick myotubes, B.f. III inhibited carbachol-induced influx of 86Rb (IC50 = 5 X 10(-9) M) at concentrations higher than those needed for alpha-bungarotoxin (IC50 = 6 X 10(-10) M).