Hobbs Joanne K, Jiao Wanting, Easter Ashley D, Parker Emily J, Schipper Louis A, Arcus Vickery L
Department of Biological Sciences, Faculty of Science and Engineering, University of Waikato , Hamilton 3240, New Zealand.
ACS Chem Biol. 2013 Nov 15;8(11):2388-93. doi: 10.1021/cb4005029. Epub 2013 Sep 17.
The increase in enzymatic rates with temperature up to an optimum temperature (Topt) is widely attributed to classical Arrhenius behavior, with the decrease in enzymatic rates above Topt ascribed to protein denaturation and/or aggregation. This account persists despite many investigators noting that denaturation is insufficient to explain the decline in enzymatic rates above Topt. Here we show that it is the change in heat capacity associated with enzyme catalysis (ΔC(‡)p) and its effect on the temperature dependence of ΔG(‡) that determines the temperature dependence of enzyme activity. Through mutagenesis, we demonstrate that the Topt of an enzyme is correlated with ΔC(‡)p and that changes to ΔC(‡)p are sufficient to change Topt without affecting the catalytic rate. Furthermore, using X-ray crystallography and molecular dynamics simulations we reveal the molecular details underpinning these changes in ΔC(‡)p. The influence of ΔC(‡)p on enzymatic rates has implications for the temperature dependence of biological rates from enzymes to ecosystems.
酶促反应速率随温度升高直至最适温度（Topt）而增加，这一现象广泛归因于经典的阿仑尼乌斯行为，而高于Topt时酶促反应速率的下降则归因于蛋白质变性和/或聚集。尽管许多研究人员指出变性不足以解释高于Topt时酶促反应速率的下降，但这种解释仍然存在。在这里，我们表明，与酶催化相关的热容变化（ΔC(‡)p）及其对ΔG(‡)温度依赖性的影响决定了酶活性的温度依赖性。通过诱变，我们证明酶的Topt与ΔC(‡)p相关，并且ΔC(‡)p的变化足以改变Topt而不影响催化速率。此外，使用X射线晶体学和分子动力学模拟，我们揭示了ΔC(‡)p这些变化背后的分子细节。ΔC(‡)p对酶促反应速率的影响对从酶到生态系统的生物速率的温度依赖性具有重要意义。
