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Thomas Hoye
Chemistry
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The sea lamprey has been around for 400 million years,
so it's a safe bet the parasitic eel-like fish comes equipped with
top-of-the-line survival tools. But the scourge of the Great Lakes
may finally have met its match.
Chemistry professor Thomas Hoye and several graduate students in
his lab are members of a University research team intent on converting
one of the lamprey's most powerful assets into a liability. They
are collaborating with a group led by Peter Sorensen, a professor
in the Department of Fisheries, Wildlife, and Conservation Biology,
to develop a species-specific, nontoxic synthetic chemical attractant
(pheromone) as a means of controlling the sea lamprey population.
An ocean native, the lamprey invaded the Great Lakes early in the
20th century and soon decimated stocks of lake trout, whitefish,
chub, and other commercially valuable species. Although it spends
only about a year of its life as an adult parasite, each lamprey
kills on average 40 pounds of fish, according to the Great Lakes
Fishery Commission, which is responsible for sea lamprey control.
Last year alone, the U.S. and Canada spent more than $16 million
on lamprey control, primarily through the use of lampricides that
kill the larvae but also some innocent species.
As adult lampreys near the end of their lives, they have only a
few weeks in which to migrate from their normal habitat in lakes
or coastal waters to freshwater streams where they spawn. However,
only about one in 10 freshwater streams provides a suitable spawning
ground and nursery habitat for larval lampreys, which spend three
to 20 years burrowed into the streambed. Adults locate these streams
by following the scent of a powerful pheromone emitted by the toothless,
blind larvae.
The pheromone works so well that simply using extracts of water
from larval lamprey nurseries improved adult attraction rates sixfold
during experiments in Michigan streams. However, the protocols for
isolating even the crude pheromone from huge volumes of stream water
are so cumbersome that this approach is unlikely to support the
needs of a large-scale, pheromone-based control program. Given the
extract's potency, the scientists reasoned, a synthetic version
of the pure pheromone would be even more effective in luring migrating
lampreys to traps where they could be sterilized, killed, or moved
to streams unsuitable for spawning.
Sorensen spent more than a decade testing the hypothesis that a
pheromonal cue guided migratory adult lampreys to spawning sites.
Using mass spectrometry his team had detected the pheromone's three
primary components, two of which were unknown. The next step was
to isolate samples of each of the pheromone's chemical components
for analysis.
That's when Hoye and his team joined the study. About four years
ago Jared Fine, then a beginning graduate researcher in Sorensen's
group, sought Hoye's expertise in nuclear magnetic resonance (NMR)
spectroscopy, a nondestructive analytical tool for determining precise
chemical structure.
After purifying 8,000 liters of water from holding tanks containing
35,000 larvae, Fine obtained only 600 to 700 micrograms of a fine
white powder-the equivalent of about 10 grains of salt. But it was
enough.
"NMR spectroscopy is a sufficiently sensitive technique, so
you need only a tiny amount," said Hoye. "And it's nondestructive,
which means that after we had finished our analysis I could return
the samples to Jared intact for subsequent biological studies."
Matching the NMR data to known spectral patterns, Hoye and students
Vadims Dvornikovs, Christopher Jeffrey, and Jizhou Wang identified
the two components and pieced together their molecular structure.
They discovered that the most abundant pheromonal component, petromyzonamine
disulfate (PADS), has a structure similar to that of squalamine,
a chemical produced by the dogfish shark. Using that information
as a resource, Dvornikovs and Jeffrey, together with students Feng
Shao and Kari Anderson, produced a small amount of synthetic PADS-about
six milligrams to date. This initial synthesis required a linear
sequence of nine chemical reactions and took nearly a year to develop.
To hoodwink the sea lamprey's keen sense of smell, a synthetic compound
must replicate the natural pheromone precisely. Of the chemical
produced in his lab Hoye said,"It is exactly the same in every
way. Not even the animal can distinguish it from nature's version."
PADS is extremely potent. A pound of it (about 500 grams) could
treat the volume of water that spills over Niagara Falls in a month-at
the rate of 100,000 cubic feet of water per second. However, laboratory
tests suggest that the pheromone may function even more effectively
as a mixture. Even at elevated concentrations, a single component
generated less lamprey activity than the larval water extract.
In November 2004 Hoye and Sorensen filed a patent application on
PADS. The researchers' findings mark the discovery of the first
migratory pheromone identified in a fish.
Currently, Hoye is conducting studies to synthesize the second major
component, petromyzosterol disulfate. The next challenge will be
to refine the synthesis of the pheromone so that large-scale production
is affordable. Hoye expects that process to take between two and
three years.
"Personally, the most rewarding part of this work has been
to watch my students grow and develop into really skilled chemists
in a context that likely will have a direct benefit," Hoye
said. "It's great to have a hand in something that may actually
get used."
The research was supported by the University's Agricultural Experiment
Station, the National Institutes of Health, and the Great Lakes
Fishery Commission.
Written by Carolyn Wavrin
Reprinted with permission from the winter 2006 edition of Inventing
Tomorrow, a publication of the Institute of Technology.
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