Malmström B G, Andréasson L E
J Inorg Biochem. 1985 Mar-Apr;23(3-4):233-42. doi: 10.1016/0162-0134(85)85030-3.
A minimal catalytic cycle for cytochrome c oxidase has been suggested, and the steady-state kinetic equation for this mechanism has been derived. This equation has been used to simulate experimental data for the pH dependence of the steady-state kinetic parameters, kcat and Km. In the simulations the rate constants for binding and dissociation of cytochrome c and for two internal electron-transfer steps have been allowed to vary, whereas fixed experimental values (for pH 7.4) have been used for the other rate constants. The results show that the dissociation of the product, ferricytochrome c, cannot be rate-limiting under all conditions, but that intramolecular electron-transfer steps also limit the rate. They also demonstrate that Km can differ considerably from the dissociation constant for the cytochrome c-oxidase complex. Published values for the rate constant for the dissociation of ferricytochrome c are too small to account for the steady-state rates. It is suggested that, at high concentrations, ferryocytochrome c transfers an electron to a cytochrome c molecule which remains bound to the oxidase. This can also explain the nonhyperbolic kinetics, which is observed at low substrate concentrations.
已经提出了细胞色素c氧化酶的最小催化循环，并推导了该机制的稳态动力学方程。该方程已用于模拟稳态动力学参数kcat和Km对pH依赖性的实验数据。在模拟中，细胞色素c结合和解离以及两个内部电子转移步骤的速率常数被允许变化，而其他速率常数则使用固定的实验值（pH 7.4时）。结果表明，产物高铁细胞色素c的解离在所有条件下都不是限速步骤，但分子内电子转移步骤也限制了速率。它们还表明，Km可能与细胞色素c - 氧化酶复合物的解离常数有很大差异。已发表的高铁细胞色素c解离速率常数的值太小，无法解释稳态速率。有人提出，在高浓度下，高铁细胞色素c将电子转移到仍与氧化酶结合的细胞色素c分子上。这也可以解释在低底物浓度下观察到的非双曲线动力学。
