High pressure & low temperature study of the mechanism of enzymatic hydrogen tunnelling: promoting motions vs multiple kinetically distinct substates

生命系统中的所有反应都是由蛋白质催化剂介导和加速的。大自然的催化剂所实现的速率加速通常高达20个数量级。了解酶加速化学反应的机制对许多学科和行业都至关重要。一般来说，当将反应物与生成物分离的反应活化能降低时，每个反应的速率都会增加。最近已经很清楚，像电子、质子、氢原子和氢化物离子这样的粒子也可以穿过这个激活势垒，从而避免了爬上激活势垒的需要。这些隧穿反应发生的机制一直是许多争论的主题。有几个研究小组用一个理论模型来解释实验观察到的反应速率对温度的依赖性。该模型认为酶的动态运动与实际反应相结合，从而促进了实际反应。这样的模型可以解释许多实验结果。然而，目前仍有许多争议，对这一模型进行测试是很重要的。此外，我们和其他人提出了其他的解释，这些解释是基于许多酶并不只有一个刚性和明确定义的构象，而是由具有不同催化性质的相似但结构不同的基态组成的集合。这是一个概念上不同的，更经典的酶的观点，应该允许解释许多观察。这里提出的工作不仅将阐明物理科学的一个基本问题，而且最终将导致在非生理环境中显示活性的人工催化剂的设计，以及在医疗保健和农业中具有许多益处的酶抑制剂。

All reactions in living systems are mediated and speeded by protein catalysts. The rate accelerations achieved by Nature's catalysts are often as high as 20 orders of magnitude. An understanding of the mechanisms by which enzymes accelerate chemical reactions is of central importance for a wide range of disciplines and industries. In general terms the rate of every reaction is increased when the activation energy for this reaction, which separates the reactants from the products, is reduced. It has recently become clear that particles like electrons, protons, hydrogen atoms, and hydride ions can also tunnel through this activation barrier thereby avoiding the need to climb the activation barrier. The mechanism by which these tunnelling reactions occur has been the subject of much debate. Several groups have used a theoretical model to explain the experimentally observed dependence of the reactions rates on temperature. This model proposes that the dynamic motions of the enzyme couple to the actual reaction and thereby promote it. Such a model could explain many experimental results. However, there are still many controversies and it is important to test this model. In addition, we and others have proposed alternative explanations which are based on the observations that many enzymes do not have only one rigid and well defined conformation, but are made up of an ensemble of similar but structurally distinct substates which have different catalytic properties. This is a conceptionally different and more classical view of enzymes which should allow the explanation of many observations. The work proposed here will not only shed light on a fundamental problem of physical sciences, but should eventually lead to the design of artificial catalysts, which display activity in non-physiological environments, and of enzyme inhibitors with many benefits in health care and agriculture.