Sept. 29, 2010
UI chemists publish findings on how enzyme motion affects chemical reactions
University of Iowa chemists have published a paper on how the motions of enzymes affect the chemical reactions they facilitate, in the hope their work will one day lead to a better understanding of enzymes and the discovery of new pharmaceuticals.
The paper appeared in the Sept. 27 online edition of the journal Proceedings of the National Academy of Sciences.
Co-authors Jigar N. Bandaria, Samrat Dutta, Michael W. Nydegger, William Rock, Amnon Kohen and Christopher M. Cheatum are all of the UI Department of Chemistry in the College of Liberal Arts and Sciences and the Optical Sciences and Technology Center.
For years, scientists have debated whether enzyme motions lasting for as brief a period of time as a picosecond (one trillionth of a second) can affect chemical reactions, partly because of the difficulty of measuring the phenomena, according to Cheatum, assistant professor of chemistry.
However, the Iowa researchers successfully used two-dimensional infrared spectroscopy to study the motions of the enzyme "formate dehydrogenase" in complexes that closely mimic the structure present at the exact moment of the chemical conversion from reactants to products.
The results showed that the enzyme's transition-state structure is different during the reaction than before or after the event. In effect, the enzyme becomes well-organized for the reaction.
"Unexpectedly, we found that the active site of the enzyme is rigid for times longer than a few picoseconds," Cheatum said. "This unique behavior shows that the motions of enzymes at the critical moment of the reaction are very different from the motions that are present in the enzyme when it is not reacting.
"These results will be important to understanding how enzymes work at the molecular level and will have potential applications in the discovery of new pharmaceuticals," he said.
Cheatum said that in the future, the researchers plan to study a series of site-selected mutants to directly correlate the dynamics they observe in the transition-state analog complexes to the kinetic isotope effect for the catalyzed reaction.
Their work was funded by a grant from the National Science Foundation, the National Institutes of Health and the Roy J. Carver Charitable Trust.
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