Methionine Ligand Lability in Bacterial Monoheme Cytochromes c: An Electrochemical Study

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• 作者：Benjamin D. Levin ; Mehmet Can ; Sarah E. J. Bowman ; Kara L. Bren ; Sean J. Elliott
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：October 13, 2011
• 年：2011
• 卷：115
• 期：40
• 页码：11718-11726
• 全文大小：946K
• 年卷期：v.115,no.40(October 13, 2011)
• ISSN：1520-5207

文摘

The direct electrochemical analysis of adsorbed redox active proteins has proven to be a powerful technique in biophysical chemistry, frequently making use of the electrode material pyrolytic 鈥渆dge-plane鈥?graphite. However, many heme-bearing proteins such as cytochromes c have been also examined systematically at alkanethiol-modified gold surfaces, and previously we reported the characterization of the redox properties of a series of bacterial cytochromes c in a side-by-side comparison of carbon and gold electrode materials. In our prior findings, we reported an unanticipated, low potential (E_m 鈭?00 mV vs SHE) redox couple that could be analogously observed when a variety of monoheme cytochromes c are adsorbed onto carbon-based electrodes. Here we demonstrate that our prior phenomological data can be understood quantitatively in the loss of the methionine ligand of the heme iron, using the cytochrome c from Hydrogenbacter thermophilum as a model system. Through the comparison of wild-type protein with M61H and M61A mutants, in direct electrochemical analyses conducted as a function of temperature and exogenous ligand concentration, we are able to show that Met-ligated cytochromes c have a propensity to lose their Met ligand at graphite surfaces, and that energetics of this process (6.3 卤 0.2 kJ/mol) is similar to the energies associated with 鈥渇oldons鈥?of known protein folding pathways.