Spectroscopic studies of myoglobin at low pH: heme ligation kinetics.
Spectroscopic studies of myoglobin at low pH: heme ligation kinetics.
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低 pH 下肌红蛋白的光谱研究：血红素连接动力学。
DOI：
10.1021/bi00219a011
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Champion,PM
中科院分区：
文献类型：
--
作者：
Sage,JT;Li,PS;Champion,PM
J. Timothy Sage，Pusheng Li和Paul M. Champion* 物理系，东北大学，波士顿，马萨诸塞州02115接收1990年5月14日;修订的Mandarin pt接收1990年10月2日摘要：在血红素结构和平衡连接的表征的基础上，我们探索肌红蛋白低于pH 4的近端和远端连接动力学。在光解的MbCO，一个显着的五坐标血红素人口观察到，与一个完整的铁组氨酸键，持续的时间尺度上的CO重新绑定。不完全的CO光解归因于四配位血红素的快速交换少数群体，这导致快速（> 1010 s-1）的成对重组。这种机制在pH 7的可能相关性也被注意到。利用一种新的实验方案，我们观察到部分光解的MbCO的共振拉曼光谱作为连续波照射时间（r）的函数。在延长光照下（r~ 35 ms，pH 3.4），拉曼光谱的v4区强度减弱，铁-组氨酸模式从五配位光产物光谱中消失。在CO束缚分数的Fe-CO伸缩区，526-cm ~（-1）模的强度增加，而491-cm ~（-1）模的强度降低。这些变化被解释为是由于连续照明下的近端组氨酸配体的替换。完全放松到纯的四坐标脱氧血红素结构中观察到的平衡是没有观察到，甚至作为-1，大概是因为CO重新绑定导致酸化的铁和它的络合物与组氨酸。我们提出了一个动力学模型来解释我们的结果，并讨论了以前的低pH动力学测量的影响。
J. Timothy Sage, Pusheng Li, and Paul M. Champion* Department of Physics, Northeastern University, Boston, Massachusetts 02115 Received May 14, 1990; Revised Manuscript Received October II, 1990 abstract: On the basis of the characterization of heme structure and ligation in equilibrium, we explore both proximal and distal ligation kinetics of myoglobin below pH 4. Upon photolysis of MbCO, a significant five-coordinate heme population is observed, with an intact iron-histidine bond that persists on the time scale of CO rebinding. Incomplete CO photolysis is attributed to a rapidly exchanging minority population of four-coordinate hemes, which leads to fast (> 1010 s'1) geminate recombination. The possible relevance of such a mechanism at pH 7 is also noted. Using a novel experimental protocol, we observe the resonance Raman spectrum of partially photolyzed MbCO as a function of continuous wave illumination time (r). Under extended illumination (r~ 35 ms at pH 3.4), there is a loss of intensityin the v4 region of the Raman spectrum and the iron-histidine mode is bleached from the spectrum of the five-coordinate photoproduct. In the Fe-CO stretching region of the CO-boundfraction, the intensity of the 526-cm'1 mode increases with at the expense of the 491-cm'1 mode. These changes are interpreted as being due to replacement of the proximal histidine ligand under continuous illumination. Complete relaxation to the pure four-coordinate deoxy heme structure observed in equilibrium is not observed even as—1, presumably since CO rebinding leads to acidification of the iron and its complexation with histidine. We propose a kinetic model to account for our results and discuss the implications for previous low-pH kinetics measurements.