Alberty Robert A
Department of Chemistry, Masssachusetts Institute of Technology, Cambridge, MA 02139, USA.
Biophys Chem. 2007 Dec;131(1-3):71-9. doi: 10.1016/j.bpc.2007.09.005. Epub 2007 Sep 19.
Rapid-equilibrium rate equations for enzyme-catalyzed reactions are especially useful when the mechanism involves a number of pKs, but they are also useful when some reactants have stoichiometric numbers greater than one or hydrogen ions are produced or consumed in the rate-determining step. The pH dependencies of limiting velocities, Michaelis constants, and reaction velocities for the forward reaction are discussed for two examples of reductase reactions of the type mR + O -> products, where R is the reductant and O is the oxidant. For the nitrate reductase reaction (EC 1.9.6.1), m = 2 and two hydrogen ions are consumed. For the nitrite-ferredoxin reductase reaction (EC 1.7.7.1), m = 6 and eight hydrogen ions are consumed. The expressions for the limiting velocities, Michaelis constants, and rate equations for the forward reaction are derived for two ordered mechanisms and the random mechanism. Three Mathematica programs are used to make plots of kinetic parameters as functions of pH and three-dimensional plots of rapid-equilibrium velocities as functions of [O] and [R] for arbitrary sets of input parameters.
当酶催化反应的机制涉及多个pK值时，快速平衡速率方程特别有用，但当某些反应物的化学计量数大于1，或者在速率决定步骤中产生或消耗氢离子时，它们也很有用。对于mR + O -> 产物类型的还原酶反应的两个例子，讨论了正向反应的极限速度、米氏常数和反应速度对pH的依赖性，其中R是还原剂，O是氧化剂。对于硝酸还原酶反应（EC 1.9.6.1），m = 2且消耗两个氢离子。对于亚硝酸铁氧化还原蛋白还原酶反应（EC 1.7.7.1），m = 6且消耗八个氢离子。推导了两种有序机制和随机机制的正向反应的极限速度、米氏常数和速率方程的表达式。使用三个Mathematica程序绘制动力学参数随pH的变化图，以及任意输入参数集下快速平衡速度随[O]和[R]的三维图。
