1 research outputs found
Drastic Compensation of Electronic and Solvation Effects on ATP Hydrolysis Revealed through Large-Scale QM/MM Simulations Combined with a Theory of Solutions
Hydrolysis of adenosine
triphosphate (ATP) is the “energy
source” for a variety of biochemical processes. In the present
work, we address key features of ATP hydrolysis: the relatively moderate
value (about −10 kcal/mol) of the standard free energy, Δ<i>G</i><sub>hyd</sub>, of reaction and the insensitivity of Δ<i>G</i><sub>hyd</sub> to the number of excess electrons on ATP.
We conducted quantum mechanical/molecular mechanical simulation combined
with the energy-representation theory of solutions to analyze the
electronic-state and solvation contributions to Δ<i>G</i><sub>hyd</sub>. It was revealed that the electronic-state contribution
in Δ<i>G</i><sub>hyd</sub> is largely negative (favorable)
upon hydrolysis, due to the reduction of electrostatic repulsion accompanying
the breakage of the P–O bond. In contrast, the solvation effect
was found to be strongly more favorable on the reactant side. Thus,
we showed that a drastic compensation of the two opposite effects
takes place, leading to the modest value of Δ<i>G</i><sub>hyd</sub> at each number of excess electrons examined. The computational
analyses were also conducted for pyrophosphate ions (PPi), and the
parallelism between the ATP and PPi hydrolyses was confirmed. Classical
molecular dynamics simulation was further carried out to discuss the
effect of the solvent environment; the insensitivity of Δ<i>G</i><sub>hyd</sub> to the number of excess electrons was seen
to hold in solvent water and ethanol