Isolation of a pure toxic polypeptide from the venom of the spider Phoneutria nigiventer and its neurophysiological activity on an insect femur preparation

The venom of the South American spider Phoneutria nigriventer has been separated into eleven fractions by gel filtration. The neurophysiological activity of each fraction was tested by perfusion of a locust femur preparation. From one of the polypeptide-containing fractions, a pure, almost neutral polypeptide was isolated and shown to have a molecular weight between 5500 and 5900. The amino acid composition of the pure polypeptide was determined. When the polypeptide (2 x 10 super(-7)M) was perfused through the locust femur preparation, action potentials were generated along the length of the axons in the crural nerve, resulting in very rapid and uncontrolled twitching of the skeletal muscles. At higher concentrations, the crural nerve discharged repetitively, both spontaneously and in response to a single electrical stimulus. The other polypeptide fractions, although less pure, had neurophysiological responses similar to those observed with the pure polypeptide; the effects of some fractions could be reversed.