Molecular size of the tetrodotoxin binding site estimated by irradiation inactivation.

Abstract

MUCH attention has been directed towards the solubilization and subsequent characterization of functional membrane components in excitable tissues, such as the sodium pump, acetylcholine receptor, and the sodium conduction channel. An alternative approach, which has been successfully applied to estimating the molecular size of Na-K activated ATPase1,2, uses irradiation inactivation analysis, and determines the target size of membrane components in situ in lyophilized preparations. The validity of this technique as applied to biological molecules has been established by a number of investigators1–3. Here we studied inactivation by irradiation with high energy electrons to estimate the molecular size of the tetrodotoxin (TTX) binding site in nervous tissue. TTX is a specific inhibitor of nerve conduction, and there is much evidence4 for the specific interaction of the toxin with the sodium conduction channel.