Interactions of CuB with Carbon Monoxide in Cytochrome c Oxidase: Origin of the Anomalous Correlation between the Fe鈥揅O and C鈥揙 Stretching Frequencies

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• 作者：Tsuyoshi Egawa ; Jonah Haber ; James A. Fee ; Syun-Ru Yeh ; Denis L. Rousseau
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：July 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：8509-8520
• 全文大小：540K
• ISSN：1520-5207

文摘

In heme鈥揷opper oxidases, the correlation curve between the iron鈥揅O and C鈥揙 stretching vibrational modes (谓_Fe鈥揅O and 谓_C鈥揙, respectively) is anomalous as compared to the correlation in other heme proteins. To extend the correlation curve, the resonance Raman (RR) and infrared (IR) spectra of the CO adducts of cytochrome ba₃ (ba₃) from Thermus thermophilus were measured. The RR spectrum has two strong 谓_Fe鈥揅O lines (508 and 515 cm^鈥?) and a very weak line at 526 cm^鈥?, and the IR spectrum has three 谓_C鈥揙 lines (1966, 1973, and 1981 cm^鈥?), indicating the presence of multiple conformers. Employing photodissociation methods, the 谓_Fe鈥揅O RR and 谓_C鈥揙 IR lines were assigned to each conformer, enabling the establishment of a reliable inverse correlation curve for the 谓_Fe鈥揅O versus the 谓_C鈥揙 stretching frequencies. To determine the molecular basis of the correlation, a series of DFT calculations on 6-coordinate porphyrin鈥揅O compounds and a model of the binuclear center of the heme鈥揷opper oxidases were carried out. The calculations demonstrated that the copper unit model caused significant mixing among porphyrin鈥揅O molecular orbitals (MOs) that contribute to the Fe鈥揅 and C鈥揙 bonding interactions, and also indicated the presence of mixing between the d_z² orbital of the copper and MOs that are responsible for the 谓_Fe鈥揅O vs 谓_C鈥揙 inverse correlation. Together, the spectroscopic and DFT results clarify the origin of the anomaly of 谓_Fe鈥揅O and 谓_C鈥揙 frequencies in the heme鈥揷opper oxidases, a long-standing issue.