期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 26, 页码 10774-10779出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0702188104
关键词
enzyme kinetics; kinetic isotope effects; quantum dynamics; molecular modeling; ensemble-averaged variational transition state theory
资金
- FIC NIH HHS [R03 TW001212, TW01212-01] Funding Source: Medline
- NIDDK NIH HHS [R01 DK045776, DK45776] Funding Source: Medline
Hydrogen transfer reactions catalyzed by coenzyme B-12-dependent methylmalonyl-CoA mutase have very large kinetic isotope effects, indicating that they proceed by a highly quantal tunneling mechanism. We explain the kinetic isotope effect by using a combined quantum mechanical/molecular mechanical potential and semiclassical quantum dynamics calculations. Multidimensional tunneling increases the magnitude of the calculated intrinsic hydrogen kinetic isotope effect by a factor of 3.6 from 14 to 51, in excellent agreement with experimental results. These calculations confirm that tunneling contributions can be large enough to explain even a kinetic isotope effect > 50, not because the barrier is unusually thin but because corner-cutting tunneling decreases the distance over which the system tunnels without a comparable increase in either the effective potential barrier or the effective mass for tunneling.
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