REBINDING AND RELAXATION IN THE MYOGLOBIN POCKET
REBINDING AND RELAXATION IN THE MYOGLOBIN POCKET
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DOI：
10.1016/0301-4622(87)80034-0
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发表时间：
1987-05-09
影响因子：
3.8
通讯作者：
YOUNG, RD
中科院分区：
文献类型：
--
作者：
ANSARI, A;BERENDZEN, J;YOUNG, RD
本文研究了羧肌红蛋白（MbCO）在10 ~ 300 K温度范围内光解后的红外拉伸带和CO与Mb的再结合。四条伸展带表明MbCO可以存在于4种底物A0-A3中。四个波段强度的温度依赖性产生了相对的结合焓和熵。谱带的综合吸光度和pH依赖关系允许用x射线数据中观察到的构象识别底物（Kuriyan等人，J. Mol. Biol. 192(1986) 133）。在低pH下，A0与His E7成氢键。底物A0-A3在75%甘油/水溶剂中可在180k以上相互转化，在缓冲水中可在270k以上相互转化。如果MbCO嵌入固体聚乙烯醇基质中，则在任何温度下都不会发生主要的相互转化。这种转变对溶剂特性的依赖被解释为从化玻璃转变。在低温下光解作用后，CO位于血红素口袋B中，由此产生的CO拉伸带被识别为B底物，与A底物的拉伸带发生蓝移。在40 K下，研究了闪光光解后的再结合在Soret，近红外和集成的A和B底物上。所有数据都位于同一条重结合曲线上，并证明了重结合在时间上是非指数的，至少从100 ks到100 ms不等。没有发现离散指数的证据。在红外区监测下，闪光光解显示出口袋B到结合底物Ai的四种不同途径。四种途径中的每一种都重新结合。A在至少10 K时是非指数的，在180 K以下，四种途径的动力学不同。根据重结合的时间和温度依赖性，提取了活化焓分布g（HBA）和指前指数ABA。在180 K以下的转变温度下，没有观察到从一个A衬底到另一个，或从一个B衬底到另一个的抽运现象。如果MbCO暴露在强烈的白光下10-103秒后才被激光完全光解，则长寿命态的振幅增加。这种效应是根据子状态的层次和子状态对称性破缺来解释的。血红素袋内CO拉伸带和再结合过程的特征在很大程度上取决于溶剂、pH和压力等外部参数。这种敏感性提示了蛋白质反应可能的控制机制。
The infrared stretching bands of carboxymyoglobin (MbCO) and the rebinding of CO to Mb after photodissociation have been studied in the temperature range 10-300 K in a variety of solvents. Four stretching bands imply that MbCO can exist in four substrates, A0-A3. The temperature dependences of the intensities of the four bands yield the relative binding enthalpies and entropies. The integrated absorbances and pH dependences of the bands permit identification of the substrates with the conformations observed in the X-ray data (Kuriyan et al., J. Mol. Biol. 192 (1986) 133). At low pH, A0 is hydrogen-bonded to His E7. The substrates A0-A3 interconvert above about 180 K in a 75% glycerol/water solvent and above 270 K in buffered water. No major interconversion is seen at any temperature if MbCO is embedded in a solid polyvinyl alcohol matrix. The dependence of the transition on solvent characteristics is explained as a slaved glass transition. After photodissociation at low temperature the CO is in the heme pocket B. The resulting CO stretching bands which are identified as B substrates are blue-shifted from those of the A substrates. At 40 K, rebinding after flash photolysis has been studied in the Soret, the near-infrared, and the integrated A and B substrates. All data lie on the same rebinding curve and demonstrate that rebinding is nonexponential in time from at least 100 ks to 100 ms. No evidence for discrete exponential is found. Flash photolysis with monitoring in the infrared region shows four different pathways within the pocket B to the bound substrates Ai. Rebinding in each of the four pathways B .fwdarw. A is nonexponential in time to at least 10 ks and the four pathways have different kinetics below 180 K. From the time and temperature dependence of the rebinding, activation enthalpy distributions g(HBA) and preexponentials ABA are extracted. No pumping from one A substrate to another, or one B substrate to another, is observed below the transition temperature of about 180 K. If MbCO is exposed to intense white light for 10-103 s before being fully photolyzed by a laser flash, the amplitude of the long-lived states increases. The effect is explained in terms of a hierarchy of substates and substate symmetry breaking. The characteristics of the CO stretching bands and of the rebinding processes in the heme pocket depends strongly on the external parameters of solvent, pH and pressure. This sensitivity suggests possible control mechanisms for protein reactions.