AMINO-ACID-SEQUENCE OF TSTX-V, AN ALPHA-TOXIN FROM TITYUS-SERRULATUS SCORPION-VENOM, AND ITS EFFECT ON K-CELLS FROM ISOLATED RAT ISLETS OF LANGERHANS( PERMEABILITY OF BETA)

Highly purified Tityustoxin V (TsTX-V), an alpha-toxin isolated from t he venom of the Brazilian scorpion Tityus serrulatus, was obtained by ion exchange chromatography on carboxymethylcellulose-52. It was shown to be homogeneous by reverse phase high performance liquid chromatogr aphy, N-terminal sequencing (first 39 residues) of the reduced and alk ylated protein and by polyacrylamide gel electrophoresis in the presen ce of sodium dodecylsulfate and tricine. Following enzymatic digestion , the complete amino acid sequence (64 residues) was determined. The s equence showed higher homology with the toxins from the venoms of the North African than with those of the North and South American scorpion s. Using the rate of Rb-86(+) release from depolarized rat pancreatic beta-cells as a measure of K+ permeability changes, TsTX-V (5.6 mu g/m l) was found to increase by 2.0-2.4-fold the rate of marker outflow in the presence of 8.3 mM glucose. This effect was persistent and slowly reversible, showing similarity to that induced by 100 mu-M veratridin e, an agent that increases the open period of Na+ channels, delaying t heir inactivation. It is suggested that, by extending the depolarized period, TsTX-V indirectly affects beta-cell voltage-dependent K+ chann els, thus increasing K+ permeability.