• Title/Summary/Keyword: high-pressure kinetics

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Effect of Pressure and Solvent Dielectric Constant on the Kinetic Constants of Trypsin-Catalyzed Reaction. (Trypsin 반응에 대한 용매의 유전상수 및 압력의 영향)

  • Park, Hyun;Chi, Young-Min
    • Microbiology and Biotechnology Letters
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    • v.28 no.1
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    • pp.26-32
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    • 2000
  • Electrostatic forces contribute to the high degree of enzyme transition state complementarity in enzyme catalyzed reaction and such forces are modified by the solvent through its dielectric constant and polar properties. The contributions of electrostatic interaction to the formation of ES complex and the stabilization of transition state of the trypsin catalyzed reaction were probed by kinetic studied with high pressure and solvent dielectric constant. A good correlation has been observed between the increase of catalytic efficiency of trypsin and the decrease of solvent dielectric constant. Activation volume linearly decreased as the dielectric constant of solvent decreased, which means the increase in the reaction rae. Moreover, the decrease of activation volume by lowering the solvent dielectric constant implies a solvent penetration of the active with and a reduction of electrostatic energy for the formation of dipole of the active site oxyanion hole. When the 야electric constant of the solvents was lowered to 4.7 unit, the loss of activation energy and that of free energy of activation were 2.262 KJ/mol and 3.169 KJ/mol, respectively. The results of this study indicate that the high pressure kinetics combined with solvent effects can provide unique information on enzyme reaction mechanisms, and the controlling the solvent dielectric constant can stabilize the transition state of the trypsin-catalyzed reaction.

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Relationship Between Enhancement of Electrostriction and Decrease of Activation Energy in Porcine Pancreatic Lipase Catalysis

  • PARK HYUN;LEE KI-SEOG;PARK SEON-MI;LEE KWANG-WON;KIM AUGUSTINE YONGHWI;CHI YOUNG-MIN
    • Journal of Microbiology and Biotechnology
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    • v.15 no.3
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    • pp.587-594
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    • 2005
  • 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 $k_{cat}$ 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.