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Colorado State Researcher Analyzes Venom Of Gila Monster; Unusual Toxin Has Chemical That Might Control Blood Pressure

Friday, March 27, 1998

FORT COLLINS--A Colorado State University biochemist has analyzed the chemical structure of venom secreted by Gila monsters and Mexican beaded lizards, a discovery that sheds light on the world's only two poisonous lizards and that eventually may help control blood pressure in humans.

Anthony Tu, professor of biochemistry and molecular biology and authority on snake venom, said the substance, called Horridum toxin after the Latin species name for the Mexican beaded lizard, shows two interesting characteristics. It is not a neurotoxin, as most snake, spider and insect venoms are, and it bears a close chemical resemblance to kallikrein, an enzyme in the human body that stimulates release of another substance, bradykinin, that lowers blood pressure in humans.

"If one eliminates the toxic action, it may have positive results for blood-pressure control, "said Tu. However, "At this point, I doubt it will do much good for the general public because it's so toxic."

Horridum toxin is, along with Gila toxin, a component of the venom of both lizards. The former is unusual in several respects. A huge protein, it is comprised of 210 amino acids (Gila toxin is made up of 245) and causes hemorrhaging in the eye.

"It's the only toxin I know of that shows such an effect," said Tu.

Both lizards have a fierce bite. Venom flows from glands along grooves in the lizards' teeth and is introduced into prey-- lizards feed on small mammals and birds--as the predator chews. Although painful, Gila monster bites are rarely fatal to adult humans.

Tu, who taught at Utah State University for five years before joining Colorado State in 1967, became interested in Gila monsters because they're native to southern Utah and because of their relatively close relationship to snakes.

"I was curious to see how they differed," said Tu, who conducted the research with postdoctoral fellow Geeta Datta. "When we started we thought the venom was neurotoxic, but it's not neurotoxic at all."

Rather than work with live lizards, which are not endangered species but are viewed as somewhat threatened, Tu purchased the venom of Gila monsters for $7,000 per gram--about 1/28th of an ounce--and switched to venom of the Mexican beaded lizard, the Gila's cousin, both because it was cheaper and because available Gila venom sources dried up.

"I used up the whole U.S. supply," he said. "Not many people are interested in it, so there wasn't much in stock."

He will leave it to physiologists to determine how venom brings about death, but he's pleased to have worked out the complex structure of the huge protein molecule.

"I'm very happy that I identified the chemical structure of the toxin from a research standpoint," Tu said. He presented his work, supported by the National Institutes of Health, at the Rocky Mountain Regional Meeting of the American Chemical Society last week in Tucson.

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