Relationship Betwee Enhancement of Electrostriction and Decrease of Activation Evergy in Porcine Pancreatic Lipase Catalysis

The contribution of electrostriction of water moleculesto the stabilization of the negatively charged tetrahedraltransition state of a lipase-catalyzed reaction was examinedby means of kinetic studies involving high-pressure and solventdielectric constant. A good correlation was observed betweenthe increased catalytic efficiency of lipase and the decreasedsolvent dielectric constant. When the dielectric constant ofsolvents was lowered by 5.00 units, the losses of activationenergy and free energy of activation were 7.92 kJ/mol and11.24 kJ/mol, respectively. The activation volume for kcatdecreased significantly as the dielectric constant of solventdecreased, indicating that the degree of electrostriction ofwater molecules around the charged tetrahedral transitionstate has been enhanced. These observations demonstrate thatthe increase in the catalytic efficiency of the lipase reactionwith decreasing dielectric constant resulted from the stabilizationof electrostatic energy for the formation of an oxyanion hole,and that this stabilization was caused by the increase ofelectrostricted water around the charged tetrahedral transitionstate. Therefore, we conclude that the control of solventdielectric constant can stabilize the tetrahedral transition state,thus lowering the activation energy. KCI Citation Count: 5