Alberty Robert A
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Biophys Chem. 2007 Jul;128(2-3):204-9. doi: 10.1016/j.bpc.2007.04.004. Epub 2007 Apr 22.
Hydrogen ions are involved in two different ways in the thermodynamics and rapid-equilibrium kinetics of enzyme-catalyzed reactions. The two ways are through pKs and through the production or consumption of hydrogen ions in the mechanism. These ways are examined for the catalyzed reactions S=P and S+H2O=P. Since the apparent equilibrium constant K' can be calculated from the kinetic parameters by use of the Haldane equation, the treatment of the effects of pH must be consistent in thermodynamics and kinetics. This leads to a new kind of Haldane equation that involves 10(pH) or 10(-pH) in addition to the kinetic parameters when hydrogen ions are produced or consumed. These concepts are applicable to more complicated reactions and rate equations. Derivations of equations for calculating these two types of pH effects are discussed in thermodynamics and rapid-equilibrium kinetics. A computer program is used to make four plots of apparent equilibrium constants and changes in the binding of hydrogen ions in the catalyzed reaction.
氢离子在酶催化反应的热力学和快速平衡动力学中以两种不同方式参与。这两种方式分别是通过pKs以及通过反应机制中氢离子的产生或消耗。针对催化反应S=P和S+H₂O=P对这些方式进行了研究。由于表观平衡常数K'可通过使用霍尔丹方程从动力学参数计算得出，所以在热力学和动力学中对pH影响的处理必须保持一致。这就引出了一种新型的霍尔丹方程，当有氢离子产生或消耗时，该方程除了包含动力学参数外，还涉及10(pH)或10(-pH)。这些概念适用于更复杂的反应和速率方程。在热力学和快速平衡动力学中讨论了计算这两种类型pH影响的方程推导。使用一个计算机程序绘制了催化反应中表观平衡常数和氢离子结合变化的四张图。
