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KMID : 0545120050150030587
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Journal of Microbiology and Biotechnology
2005 Volume.15 No. 3 p.587 ~ p.594
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Relationship Between Enhancement of Electrostriction and Decrease of Activation Energy in Porcine Pancreatic Lipase Catalysis
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Park H
Lee KS/Park SM/Lee KW/Kim YH/Chi YM
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Abstract
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The contribution of electrostriction of water molecules to the stabilization of the negatively charged tetrahedral transition state of a lipase-catalyzed reaction was examined by means of kinetic studies involving high-pressure and solvent dielectric constant. A good correlation was observed between the increased catalytic efficiency of lipase and the decreased solvent dielectric constant. When the dielectric constant of solvents was lowered by 5.00 units, the losses of activation energy and free energy of activation were 7.92 kJ/mol and 11.24 kJ/mol, respectively. The activation volume for kcat decreased, significantly as the dielectric constant of solvent decreased indicating that the degree of electrostriction of water molecules around the charged tetrahedral transition state has been enhanced. These observations demonstrate that the increase in the catalytic efficiency of the lipase reaction with decreasing dielectric constant resulted from the stabilization of electrostatic energy for the formation of an oxyanion hole, and that this stabilization was caused by the increase of electrostricted water around the charged tetrahedral transition state. Therefore, we conclude that the control of solvent dielectric constant can stabilize the tetrahedral transition state, thus lowering the activation energy.
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