Daniel R M, Smith J C, Ferrand M, Héry S, Dunn R, Finney J L
Department of Biological Sciences, University of Waikato, Hamilton, New Zealand.
Biophys J. 1998 Nov;75(5):2504-7. doi: 10.1016/S0006-3495(98)77694-5.
Enzyme activity requires the activation of anharmonic motions, such as jumps between potential energy wells. However, in general, the forms and time scales of the functionally important anharmonic dynamics coupled to motion along the reaction coordinate remain to be determined. In particular, the question arises whether the temperature-dependent dynamical transition from harmonic to anharmonic motion in proteins, which has been observed experimentally and using molecular dynamics simulation, involves the activation of motions required for enzyme function. Here we present parallel measurements of the activity and dynamics of a cryosolution of glutamate dehydrogenase as a function of temperature. The dynamical atomic fluctuations faster than approximately 100 ps were determined using neutron scattering. The results show that the enzyme remains active below the dynamical transition observed at approximately 220 K, i.e., at temperatures where no anharmonic motion is detected. Furthermore, the activity shows no significant deviation from Arrhenius behavior down to 190 K. The results indicate that the observed transition in the enzyme's dynamics is decoupled from the rate-limiting step along the reaction coordinate.
酶活性需要非谐运动的激活，例如在势能阱之间的跳跃。然而，一般来说，与沿反应坐标的运动耦合的功能重要的非谐动力学的形式和时间尺度仍有待确定。特别是，一个问题出现了，即在蛋白质中通过实验和分子动力学模拟观察到的从谐运动到非谐运动的温度依赖性动力学转变，是否涉及酶功能所需运动的激活。在这里，我们展示了谷氨酸脱氢酶冷冻溶液的活性和动力学随温度变化的平行测量。使用中子散射确定了快于约100皮秒的动态原子涨落。结果表明，在约220K观察到的动力学转变温度以下，即未检测到非谐运动的温度下，酶仍保持活性。此外，在低至190K时，活性与阿伦尼乌斯行为没有显著偏差。结果表明，观察到的酶动力学转变与沿反应坐标的限速步骤解耦。
