Prusakov V E, Steyer J, Parak F G
Fakultät für Physik E17, Technischen Universität München, Garching, Germany.
Biophys J. 1995 Jun;68(6):2524-30. doi: 10.1016/S0006-3495(95)80435-2.
A frozen solution of 57Fe-enriched metmyoglobin was irradiated by x rays at 77 K. Mössbauer spectra showed a reduction of Fe(III) high spin by thermalized electrons and a production of a metastable Fe(II) low spin myoglobin complex with H2O at its sixth coordination site. The relaxation of the intermediate was investigated by Mössbauer spectroscopy as a function of temperature and time. The relaxation process starts above 140 K and is fully completed at approximately 200 K. At temperatures between 140 and 200 K, the relaxation lasts for hours and is nonexponential in time. Up to 180 K, the process can be described satisfactorily by a gamma distribution of activation enthalpies with an Arrhenius relation for the rate coefficient. The temperature and time dependence of the Mössbauer parameters indicates structural changes in the active center of the protein as early as 109 K that continue for several hours at higher temperatures. Above 180 K, structural rearrangements involving the whole protein molecule lead to a shift and narrowing of the barrier height distribution.
富含57Fe的高铁肌红蛋白冷冻溶液在77 K下用X射线辐照。穆斯堡尔光谱显示，热电子使Fe(III)高自旋态还原，并在其第六配位位点产生了与H2O形成的亚稳态Fe(II)低自旋肌红蛋白配合物。通过穆斯堡尔光谱研究了该中间体的弛豫过程与温度和时间的关系。弛豫过程在140 K以上开始，在约200 K时完全完成。在140至200 K之间的温度下，弛豫持续数小时且时间上是非指数性的。在180 K以下，该过程可以用活化焓的伽马分布和速率系数的阿仑尼乌斯关系来令人满意地描述。穆斯堡尔参数的温度和时间依赖性表明，早在109 K时蛋白质活性中心就发生了结构变化，在较高温度下这种变化会持续数小时。在180 K以上，涉及整个蛋白质分子的结构重排导致势垒高度分布的偏移和变窄。
