butter clam



Saxitoxin (STX) is a neurotoxin naturally produced by certain species of marine dinoflagellates (Alexandrium sp., Gymnodinium sp., Pyrodinium sp.) and cyanobacteria (''Anabaena sp., Aphanizomenon sp., Cylindrospermopsis sp., Lyngbya sp., Planktothrix sp.). The term saxitoxin originates from the butter clam (Saxidomus giganteus) in which it was first recognized.


It is a neurotoxin that acts as a selective sodium channel blocker.

Human illness

The human illness associated with ingestion of harmful levels of saxitoxin is known as paralytic shellfish poisoning, or PSP, and saxitoxin and its derivatives are often referred to as "PSP toxins".

The medical and ecological importance of saxitoxin lies mainly in effects of harmful algal blooms on shellfish and certain finfish which can concentrate the toxin, making it available both for human consumption as well as by various marine organisms. The blocking of neuronal sodium channels which occurs in PSP produces a flaccid paralysis that leaves its victim calm and conscious through the progression of symptoms. Death often occurs from respiratory failure. PSP toxins have been implicated in various marine animal mortalities involving trophic transfer of the toxin from its algal source up the food web to higher predators.

Military use

It is listed in schedule 1 of the Chemical Weapons Convention. According to the book Spycraft, U-2 spyplane pilots were provided with needles containing saxitoxin to be used in the event escape was impossible. The United States military isolated saxitoxin and assigned it the chemical weapon designation TZ. Though its early isolation and characterization were related to military efforts, saxitoxin has been more important to cellular research in delineating the function of the sodium channel.

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