What is saxitoxin?

Saxitoxin is a toxin that is responsible for paralytic shell-fish poisoning during red tides. It is also found in several species of puffers and other marine animals. It was discovered in 1927. In 1975, the structure of saxitoxin was established by x-ray crystallography.

Saxitoxin is a unique compound in that it is a very specific neurotoxin. This molecule binds with very high affinity to sodium channel in excitable tissues, blocking them and thus blocking the production of action potentials. Its basic structure is that of a trialkyl tetrahydropurine, with positions 2 and 8 of the purine ring containing the NH2 groups, which form the two permanent guanidinium moieties. It possesses two pKa’s of 8.22 and 11.28, which belong to the 7, 8, 9 and 1, 2, 3 guanidinium groups, respectively.

Red tides occur when warm weather and ocean conditions allow for an abundant overgrowth or bloom of phytoplankton. Several of the phytoplankton are known to produce saxitoxin. Saxitoxin is one of the most non-protein toxins known to man.

Saxitoxin is about 1000 times more toxic than a typical synthetic nerve gas such as sarin, and about 50 times more potent that curare. Saxitoxin can be detected in environmental samples in commercial laboratories and by an enzyme-linked immunosorbent assay (ELISA) method in biologic samples.

Mild symptoms of paralytic shell-fish poisoning include a tingling sensation or numbness around the lips, gradually spreading to the face and neck, a prickly sensation in fingertips and toes, headache, dizziness and nausea.

Respiratory failure and death may occur from paralysis within 2-12 hours in untreated cases. Timely medical assistance, in the form of mechanical artificial respiration is essential.
What is saxitoxin?