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Critter Chemistry

January 27, 2003

Scorpion Uses Potassium Ions to Stun Prey

Rebecca Rawls

Scorpions have a two-part chemical arsenal that they use to stun their prey and deter enemies, according to former graduate student Bora Inceoglu, entomology professor Bruce D. Hammock, and their colleagues at the University of California, Davis [Proc. Natl. Acad. Sci. US published online Jan. 24, http://pnas.org/cgi/doi/10.1073/pnas.242735499].

DOUBLE TROUBLE Clear prevenom, shown left on tip of scorpion's tail, is visibly different from milky venom, on right, secreted later.

The first weapon, which the researchers call prevenom, is a clear liquid thatcontains roughly 80 mM potassium salt and other substances, including a peptide that blocks potassium channels in the victim, making the jolt of potassium even more toxic. This is followed, if needed, by a second and better studied milky white venom that is richin neurotoxic peptides.Although entomologistsfirst observed prevenom in scorpions more than 20 years ago, the current work is the first to show that its potency comes not from peptides, but from potassium salts.

A sting with the potassium-rich prevenom from the scorpion Parabuthus transvaalicus is even more painful than regular venom, Hammock says, though it would not kill a human as the venom can. It takes many days to weeks for a scorpion to replenish its peptide-rich venom, he notes, so the animals are very conservative about using it. Prevenom alone is enough to stun small prey or to cause tremendous pain that would deter predators, he suggests, and it's much easier for trpion to produce.

Chemical & Engineering News
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