Webb M R, Trentham D R
J Biol Chem. 1981 Nov 10;256(21):10910-6.
During ATP hydrolysis, myosin or subfragment 1 catalyzes the exchange of oxygens between water and phosphate, so that on average, each product Pi molecule contains more than one oxygen atom derived from water. Using quenched-flow techniques, the exchange process in both ATP and Pi was studied in the rabbit skeletal muscle subfragment 1 ATPase. The exchange in protein-bound ATP (M*.ATP) and protein-bound ADP.Pi (M**.ADP.Pi) was followed as a function of time. The pattern of exchange follows closely a model in which M*.ATP + H2O and M**.ADP.Pi are interconverted directly, without any characterizable intermediate between these species. All oxygen atoms of Pi are equivalent with respect to loss to solvent, and elimination of water to re-form ATP occurs with a rate constant of 15 s-1 (at pH 8.0, I 0.015 M, 20 degrees C). This is the first direct measurement of the rate constant for the transformation of M**.ADP.Pi to M*.ATP. Oxygen exchange during steady state ATP hydrolysis in the presence of acto-subfragment 1 also fits well to this model, with actin reducing the time available for M*.ATP and M**.ADP.Pi to undergo exchange.
在ATP水解过程中，肌球蛋白或亚片段1催化水与磷酸之间的氧交换，因此平均而言，每个产物Pi分子含有不止一个来自水的氧原子。使用淬灭流动技术，在兔骨骼肌亚片段1 ATP酶中研究了ATP和Pi中的交换过程。跟踪蛋白质结合的ATP（M*.ATP）和蛋白质结合的ADP.Pi（M**.ADP.Pi）中的交换随时间的变化。交换模式紧密遵循一个模型，其中M*.ATP + H2O和M**.ADP.Pi直接相互转化，在这些物种之间没有任何可表征的中间体。Pi的所有氧原子在向溶剂损失方面是等效的，并且水的消除以重新形成ATP的速率常数为15 s-1（在pH 8.0、I 0.015 M、20摄氏度下）发生。这是对M**.ADP.Pi向M*.ATP转化的速率常数的首次直接测量。在肌动蛋白-亚片段1存在下稳态ATP水解过程中的氧交换也很好地符合该模型，肌动蛋白减少了M*.ATP和M**.ADP.Pi进行交换的可用时间。
