Abstract
Electrophysiological studies with neuroblastoma cells have shown that toxin gamma from the venom of the scorpion Tityus serrulatus is a new toxin specific for the gating system of the Na+ channel. The procedure which solubilizes the tetrodotoxin receptor from rat brain also solubilizes the Tityus gamma toxin receptor. Binding experiments on the solubilized receptor with a radioiodinated derivative of Tityus gamma toxin have shown: (i) that the TiTx gamma-receptor complex is very stable with a dissociation constant of 8.6 X 10(-12) M and a very slow dissociation (T 1/2 = 15 h); (ii) that the toxin recognizes a class of sites with a 1:1 stoichiometry with those for tetrodotoxin (Bmax = 1.3 pmol/mg protein). The radioiodinated Tityus gamma-receptor complex has been substantially purified by ion-exchange chromatography, lectin affinity chromatography and sucrose gradient sedimentation. A ratio of one Tityus gamma toxin binding site per tetrodotoxin binding site was found throughout the purification. The purified material exhibited a sedimentation coefficient of 10.4S and had an apparent mol. wt. of 270 000 on SDS-gel electrophoresis. No other polypeptide chains were demonstrated to be associated with this large protein in the Tityus gamma receptor. The main conclusion is that the tetrodotoxin binding site associated with the selectivity filter of the Na+ channel and the Tityus gamma toxin binding site associated with the gating component are probably carried by the same polypeptide chain.