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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