Peterson Michelle E, Eisenthal Robert, Danson Michael J, Spence Alastair, Daniel Roy M
Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand.
J Biol Chem. 2004 May 14;279(20):20717-22. doi: 10.1074/jbc.M309143200. Epub 2004 Feb 18.
Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, T(eq), arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source ("evolved") temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, T(eq) is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on T(eq) with respect to enzyme temperature/activity effects to be more important than on thermal stability. T(eq) is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution.
酶的两个既定热特性是阿累尼乌斯活化能和热稳定性。由于发现酶活性随温度变化存在异常，已将五种不同酶的活性和稳定性特性的实验数据与理论模型进行了比较。结果为酶的一个新的基本第三热参数T(eq)提供了证据，该参数源于活性酶与无活性（或活性较低）形式之间亚秒级时间尺度上的可逆温度依赖性平衡。因此，在高于其最适温度时，由于这种平衡的温度依赖性变化导致的酶活性下降比热变性导致的下降大两个数量级。该参数对于我们理解催化活性与热稳定性之间的联系以及温度对细胞内酶反应的影响具有重要意义。与不受酶的来源（“进化”）温度影响的阿累尼乌斯活化能以及不一定与活性相关的酶稳定性不同，T(eq)对于酶在环境温度下的生理适应性至关重要，并以一种前所未有的方式将生命适应温度的分子、生理和环境方面联系起来。因此，我们可以预期进化对T(eq)在酶温度/活性效应方面的影响比在热稳定性方面更为重要。在通过合理设计和定向酶进化对酶进行热性质改造时，T(eq)也是一个需要考虑的重要参数。
