Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
Institute of Molecular Psychiatry, Rheinische-Friedrichs-Wilhelm Universität Bonn, D-53127 Bonn, Germany.
Molecules. 2023 Nov 8;28(22):7486. doi: 10.3390/molecules28227486.
The integration of phosphorus chemistry with the mechanism of ATP synthesis/hydrolysis requires dynamical information during ATP turnover and catalysis. Oxygen exchange reactions occurring at β-catalytic sites of the FF-ATP synthase/F-ATPase imprint a unique record of molecular events during the catalytic cycle of ATP synthesis/hydrolysis. They have been shown to provide valuable time-resolved information on enzyme catalysis during ATP synthesis and ATP hydrolysis. The present work conducts new experiments on oxygen exchange catalyzed by submitochondrial particles designed to (i) measure the relative rates of Pi-ATP, Pi-HOH, and ATP-HOH isotope exchanges; (ii) probe the effect of ADP removal on the extent of inhibition of the exchanges, and (iii) test their uncoupler sensitivity/resistance. The objectives have been realized based on new experiments on submitochondrial particles, which show that both the Pi-HOH and ATP-HOH exchanges occur at a considerably higher rate relative to the Pi-ATP exchange, an observation that cannot be explained by previous mechanisms. A unifying explanation of the kinetic data that rationalizes these observations is given. The experimental results in (ii) show that ADP removal does not inhibit the intermediate Pi-HOH exchange when ATP and submitochondrial particles are incubated, and that the nucleotide requirement of the intermediate Pi-HOH exchange is adequately met by ATP, but not by ADP. These results contradicts the central postulate in Boyer's binding change mechanism of reversible catalysis at a F catalytic site with Keq~1 that predicts an absolute requirement of ADP for the occurrence of the Pi-HOH exchange. The prominent intermediate Pi-HOH exchange occurring under hydrolytic conditions is shown to be best explained by Nath's torsional mechanism of energy transduction and ATP synthesis/hydrolysis, which postulates an essentially irreversible cleavage of ATP by mitochondria/particles, independent from a reversible formation of ATP from ADP and Pi. The explanation within the torsional mechanism is also shown to rationalize the relative insensitivity of the intermediate Pi-HOH exchange to uncouplers observed in the experiments in (iii) compared to the Pi-ATP and ATP-HOH exchanges. This is shown to lead to new concepts and perspectives based on ligand displacement/substitution and ligand permutation for the elucidation of the oxygen exchange reactions within the framework of fundamental phosphorus chemistry. Fast mechanisms that realize the rotation/twist, tilt, permutation and switch of ligands, as well as inversion at the γ-phosphorus synchronously and simultaneously and in a concerted manner, have been proposed, and their stereochemical consequences have been analyzed. These considerations take us beyond the binding change mechanism of ATP synthesis/hydrolysis in bioenergetics.
磷化学与 ATP 合成/水解机制的结合需要在 ATP 转化和催化过程中获取动态信息。FF-ATP 合酶/ATP 酶的β催化部位发生的氧交换反应在 ATP 合成/水解的催化循环过程中留下了分子事件的独特记录。它们已被证明可在 ATP 合成和 ATP 水解过程中提供有关酶催化的有价值的时间分辨信息。本工作针对设计的亚线粒体颗粒中的氧交换进行了新的实验,旨在 (i) 测量 Pi-ATP、Pi-HOH 和 ATP-HOH 同位素交换的相对速率;(ii) 探测 ADP 去除对交换抑制程度的影响,以及 (iii) 测试它们对解偶联剂的敏感性/抗性。这些目标是基于亚线粒体颗粒的新实验实现的,结果表明,与 Pi-ATP 交换相比,Pi-HOH 和 ATP-HOH 交换的速率都要高得多,这一观察结果无法用以前的机制来解释。给出了一个统一的解释,使这些观察结果合理化。实验结果 (ii) 表明,当 ATP 和亚线粒体颗粒孵育时,ADP 的去除不会抑制中间的 Pi-HOH 交换,并且中间的 Pi-HOH 交换的核苷酸需求可以通过 ATP 充分满足,但不能通过 ADP 满足。这些结果与 Boyer 的可逆催化绑定变化机制的中心假设相矛盾,该假设认为在 F 催化位点处,可逆催化需要 ADP 的绝对存在,才能发生 Pi-HOH 交换。水解条件下发生的显著中间 Pi-HOH 交换最好通过 Nath 的能量传递和 ATP 合成/水解扭转机制来解释,该机制假设线粒体/颗粒中 ATP 的断裂基本上是不可逆的,与 ADP 和 Pi 形成可逆的 ATP 无关。扭转机制内的解释还表明,与 Pi-ATP 和 ATP-HOH 交换相比,实验中观察到的中间 Pi-HOH 交换对解偶联剂的相对不敏感可以合理化。这导致了基于配体置换/取代和配体排列的新概念和观点,以阐明基本磷化学框架内的氧交换反应。提出了实现配体旋转/扭转、倾斜、排列和开关以及γ-磷同步、同时和协调反转的快速机制,并分析了它们的立体化学后果。这些考虑使我们超越了生物能学中 ATP 合成/水解的绑定变化机制。
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