Spectroscopic evidence for conformational relaxation in myoglobin.
Spectroscopic evidence for conformational relaxation in myoglobin.
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DOI：
10.1073/pnas.89.7.2902
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发表时间：
1992-04
影响因子：
11.1
通讯作者：
G. Nienhaus;J. Mourant;H. Frauenfelder
中科院分区：
文献类型：
--
作者：
G. Nienhaus;J. Mourant;H. Frauenfelder
用傅里叶变换红外光谱法测量了脱氧肌红蛋白（Mb）和连续光解一氧化碳肌红蛋白（MbCO）在760 nm附近的谱带III的谱线面积（M0）和位置（M1）随时间和温度的变化。低于200 K，带III的面积在光产物Mb* 随时间增加，即使在小时的时间尺度上。这种行为表明在扩展照明下配体再结合的活化焓势垒分布的变化。Mb* 的带位置随着温度的升高而移动到更高的波数，最高可达100 K，这是由于动力学烧孔;控制带III位置的相同蛋白质坐标也决定了再结合势垒高度。移动停止高于100 K，这意味着一个以上的蛋白质坐标影响的高度的再结合障碍。在160 K以上，Mb* 的线位置再次移动，并与温度高于200 K时的Mb值合并。这种转变伴随着线面积的增加，反映了再结合动力学的减缓。这两种效应都在施泰因巴赫等人[（1991）生物化学30，3988-4001]引入的模型框架中解释。在约160 K以上，构象弛豫Mb*-Mb同时移动带III的线位置，并增加配体再结合的焓垒。此外，平衡涨落导致带位置和再结合焓的平均。
The time and temperature dependencies of the line area (M0) and position (M1) of band III at approximately 760 nm have been measured with Fourier-transform infrared spectroscopy in deoxymyoglobin (Mb) and continuously photolyzed carbon monoxide myoglobin (MbCO). Below 200 K, the area of band III in the photoproduct Mb* increases with time even on time scales of hours. This behavior indicates changes in the distribution of activation enthalpy barriers for ligand rebinding under extended illumination. The band position of Mb* shifts to higher wavenumbers with increasing temperature up to 100 K owing to kinetic hole burning; the same protein coordinate that controls the position of band III also determines the rebinding barrier height. The shift ceases above 100 K, implying that more than one protein coordinate affects the height of the rebinding barrier. Above 160 K, the line position in Mb* shifts again and coalesces with the value of Mb for temperatures above 200 K. The shift is accompanied by an increase of the line area, reflecting a slowing of rebinding kinetics. Both effects are explained in the framework of the model introduced by Steinbach et al. [(1991) Biochemistry 30, 3988-4001]. Above approximately 160 K, the conformational relaxation Mb*----Mb simultaneously shifts the line position of band III and increases the enthalpy barrier for ligand rebinding. Furthermore, equilibrium fluctuations lead to an averaging of the band position and the rebinding enthalpy.