Investigations of optical line shapes and kinetic hole burning in myoglobin.
Investigations of optical line shapes and kinetic hole burning in myoglobin.
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肌红蛋白中光学线形状和动力学烧孔的研究。
DOI：
10.1021/bi00244a005
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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：
Srajer,V;Champion,PM
东北大学物理系，波士顿，马萨诸塞州，02115收到1991年2月15日；修订稿收到1991年4月29日摘要：我们介绍了对脱氧肌球蛋白(Mb)、配体结合形式(MbCO)和低温光产物(Mb*)光学线形的广泛研究结果。考虑到吸收带的基本振动性质，分析了Soret带和近红外带III(~760 nm)的热性质和与pH的关系。与MbCO的Soret带和Mb的带III相关的强烈的温度依赖性表明，与共振拉曼光谱中可能没有直接观察到的低频模式有显著的耦合。在对不同的血红素体系进行类似线形研究的基础上，我们将MbCO中的低频耦合归结为CO分子的扭转运动。耦合到带III(~70 cm~(-1))的低频模与用动力学确定的力常数值(17N/m)计算的血红素穹顶运动的值(~50 cm~(-1))非常接近。Mb和Mb*的Soret区显著的不均匀加宽被发现是由于我们与近端组氨酸的取向相关联的“非运动”坐标。Soret带和带III随体系从Mb*演化到Mb的光学驰豫随温度的变化而变化，并在185K处发现一个急剧的转变温度。Soret带和带III随Mb*演化到Mb的蓝移几乎相同(APAbs~140 cm~(-1))，归因于a的平均值在Mb*(Aj)和Mb(a0=0.45A)之间的变化。一个简单的二次型坐标耦合模型同时解释了观察到的位移，8，低温动力学和动力学烧孔，预测了血红素的室温Arrhenius势垒高度为a‘0=0.2±0.05α和=16±2kJ/mol。还发展了一种简单的定量方法来分析动力学烧孔实验，并将其应用于最近涉及四元和亚单位特定血红蛋白的研究。血红素蛋白是一类重要的生物分子，参与了广泛的基本配体结合、催化和电子传输反应。位于大分子活性部位的血红素修复基团的电子结构和共价键显然对血红素蛋白的生化活性和功能多样性起着核心作用。然而，血红素和蛋白质运动之间的相互作用也是固有的兴趣，因为周围蛋白质基质的波动和构象变化可以导致血红素几何结构的动态调节，从而影响其反应活性。作为一个具体的例子，我们考虑双原子的束缚
Department of Physics, Northeastern University, Boston, Massachusetts 02115 Received February 15, 1991; Revised Manuscript Received April 29, 1991 abstract: We present the results of an extensive investigation of the optical line shapes of deoxymyoglobin (Mb), the ligand-bound form (MbCO), and the low-temperature photoproduct (Mb*). The thermal properties and the pH dependence of the Soret band and the near infrared band III (~ 760 nm) are analyzed, taking into account the underlying vibrational properties of the absorption bands. The strong temperature dependence associated with the Soret band of MbCO and band III of Mb indicates significant coupling to low-frequency modes that may not be directly observed in the resonance Raman spectra. On the basis of analogous line-shape studies in a variety of heme systems, we assign the low-frequency coupling in MbCO to torsional motions of the CO molecule. The low-frequency mode coupled to band III (~ 70 cm" 1) is found to lie quite close to the value for the heme-doming motion (~ 50 cm" 1) calculated by using the kinetically determined value of the force constant (17 N/m). Significant inhomogeneous broadening in the Soret region of Mb and Mb* is found to be due to a “nonkinetic” coordinate that we associate with the orientation of the proximal histidine. A “kinetic” coordinate, associated with the equilibrium displacement of the iron atom from the porphyrin plane (a) is found to contribute to the inhomogeneous broadening of both the Soret band and band III. The relaxation of the heme as the systemevolves from from Mb* to Mb is followed optically as a function of temperature, and a sharp transition temperature is found at 185 K. The blue shifts of the Soret band and band III as Mb* evolves to Mb are found to be nearly identical (APAbs~ 140 cm" 1) and attributed to changes in the mean value of a between Mb*(aj) and Mb (a0= 0.45 A). A simple quadratic model for the coordinate coupling that simultaneously accounts for the observed shift, 8, the low-temperature kinetics and the kinetic hole burning predicts a'0= 0.2±0.05 Á and= 16±2 kJ/mol for the room temperature Arrhenius barrier height at the heme. A simple quantitative method for the analysis of kinetic hole-burning experiments is also developed and applied to recent studies involving quaternary and sub-unit-specific hemoglobinstructures.Heme proteins constitute an important class of biomolecules that are involved in a wide variety of fundamental ligandbinding, catalysis, and electrontransport reactions. The electronic structure and covalent linkage of the heme prosthetic group, located at the active site of the macromolecule, clearly plays a central role in the biochemical activity and functional diversity of heme proteins. Nevertheless, the interaction between the heme and the protein motions is also of inherent interest, since the fluctuations and conformational changes of the surrounding protein matrix can lead to dynamic modulations of the heme geometry that affect its reactivity. As a specific example, we consider the binding of diatomic