Biomedical Engineering Reference
In-Depth Information
The quantitized classical path approach (Hwang and Warshel, 1996) was applied to the
analysis of quantum mechanical nuclear motion in enzyme catalysis. According to this
approach the rate constant of the process
where F is the transmission factor and, is the quantum mechanical activation free
energy. The main quantum mechanical effects are associated with the exponential factors.
According to the modified Marcus relationship (Warshel et. al., 1992)
Here
is
the
nuclear
off-diagonal matrix element
where is the distance between the proton donor and acceptor groups. In the initial
proton-transfer step in the
carbonic anhydrase reaction,
and
A-1 for the oxygen - oxygen distance.
Quantum dynamics effects for hydride transfer in enzyme catalysis have been analyzed
by Alhambra et. al., 2000. This process is simulated using canonically variational
transition-states for overbarrier dynamics and optimized multidimensional paths for
tunneling. A system is divided into a primary zone (substrate-enzyme-coenzyme), which
is embedded in a secondary zone (substrate-enzyme-coenzyme-solvent). The potential
energy surface of the first zone is treated by quantum mechanical electronic structure
methods, and protein, coenzyme, and solvent atoms by molecular mechanical force fields.
The
theory
allows
the
calculation
of
Schaad-Swain
exponents for
primary
and
secondary
KIE
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