Cupane A, Vitrano E, Ormos P, Nienhaus G U
Istituto di Fisica and INFM, University of Palermo, Italy.
Biophys Chem. 1996 Jun 11;60(3):111-7. doi: 10.1016/0301-4622(96)00011-7.
We have measured the Soret band of the photoproduct obtained by complete photolysis of sperm whale carbonmonoxymyoglobin at 10 K. The experimental spectrum has been modeled with an analytical expression that takes into account the homogeneous bandwidth, the coupling of the electronic transition with both high and low frequency vibrational modes, and the effects of static conformational heterogeneity. The comparison with deoxymyoglobin at low temperature reveals three main differences. In the photoproduct, the Soret band is shifted to red. The band is less asymmetric, and an enhanced coupling to the heme vibrational mode at 674 cm-1 is observed. These differences reflect incomplete relaxation of the active site after ligand dissociation. The smaller band asymmetry of the photoproduct can be explained by a smaller displacement of the iron atom from the mean porphyrin plane, in quantitative agreement with the X-ray structure analysis. The enhanced vibrational coupling is attributed to a subtle heme distortion from the planar geometry that is barely detectable in the X-ray structure.
我们测量了抹香鲸一氧化碳肌红蛋白在10 K下完全光解得到的光产物的索雷特带。实验光谱用一个解析表达式进行了模拟，该表达式考虑了均匀带宽、电子跃迁与高频和低频振动模式的耦合以及静态构象异质性的影响。与低温下的脱氧肌红蛋白相比，发现了三个主要差异。在光产物中，索雷特带向红色移动。该带的不对称性较小，并且观察到与674 cm-1处的血红素振动模式的耦合增强。这些差异反映了配体解离后活性位点的不完全弛豫。光产物较小的带不对称性可以通过铁原子相对于平均卟啉平面的较小位移来解释，这与X射线结构分析在定量上是一致的。增强的振动耦合归因于血红素从平面几何形状的细微畸变，这种畸变在X射线结构中几乎无法检测到。
