Evidence for environmentally coupled hydrogen tunneling during dihydrofolate reductase catalysis |
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Authors: | Maglia Giovanni Allemann Rudolf K |
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Affiliation: | School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. |
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Abstract: | Hydride transfer during catalysis by dihydrofolate reductase from Thermotoga maritima has been studied by stopped flow spectroscopy. The reduction of dihydrofolate by NADPH showed a biphasic temperature dependence of the deuterium kinetic isotope effect. At temperatures above 25 degrees C the KIE was temperature independent, while the reaction rates were strongly temperature dependent. Below 25 degrees C the KIE becomes dependent on temperature, and the ratio of the preexponential factors is inverse, suggesting a greater role for active dynamics that modulate the tunneling distance. |
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