Hoek J B, Rydström J
Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
Biochem J. 1988 Aug 15;254(1):1-10. doi: 10.1042/bj2540001.
From the foregoing considerations, the energy-linked transhydrogenase reaction emerges as a powerful and flexible element in the network of redox and energy interrelationships that integrate mitochondrial and cytosolic metabolism. Its thermodynamic features make it possible for the reaction to respond readily to challenges, either on the side of NADPH utilization or on the side of energy depletion. Yet, the kinetic features are designed to prevent a wasteful input of energy when other sources of reducing equivalents to NADP are available, or to deplete the redox potential of NADPH in other than emergency conditions. By virtue of these characteristics, the energy-linked transhydrogenase can act as an effective buffer system, guarding against an excessive depletion of NADPH, preventing uncontrolled changes in key metabolites associated with NADP-dependent enzymes and calling on the supply of reducing equivalents from NAD-linked substrates only under conditions of high demand for NADPH. At the same time, it can provide an emergency protection against a depletion of energy, especially in situations of anoxia where a supply of reducing equivalents through NADP-linked substrates can be maintained. The flexibility of this design makes it possible that the functions of the energy-linked transhydrogenase vary from one tissue to another and are readily adjustable to different metabolic conditions.
基于上述考虑，能量偶联转氢酶反应在整合线粒体和胞质代谢的氧化还原与能量相互关系网络中，成为一个强大且灵活的要素。其热力学特性使该反应能够对NADPH利用方面或能量耗竭方面的挑战迅速做出响应。然而，其动力学特性旨在防止在有其他还原当量来源可用于NADP时浪费能量输入，或在非紧急情况下耗尽NADPH的氧化还原电位。凭借这些特性，能量偶联转氢酶可作为一种有效的缓冲系统，防止NADPH过度消耗，防止与NADP依赖性酶相关的关键代谢物发生失控变化，并仅在对NADPH有高需求的条件下调用来自NAD连接底物的还原当量供应。同时，它可以提供针对能量耗竭的紧急保护，特别是在缺氧情况下，此时通过NADP连接底物的还原当量供应可以维持。这种设计的灵活性使得能量偶联转氢酶的功能在不同组织之间有所不同，并能很容易地适应不同的代谢条件。
