Potency Difference between the Zwitterion Form and the Cation Forms of Tetrodotoxin
George Camougis 1,
Bertil H. Takman 1,
J. Rene 1, and
P. Tasse 1
1 Laboratory of Biological Research, Astra Pharmaceutical Products, Inc., Worcester, Massachusetts 01606
Tetrodotoxin can exist as a zwitterion or two different cations in aqueous solutions. The cation forms are more potent in nerve block. Thus the lactone-hemilactal configuration of tetrodotoxin influences potency. Electrostatic attraction, hydrogen bonding, and intermolecular hemilactal formation are possible mechanisms of interaction with membrane receptors.