Electron transfer reactions, cyanide and O₂ binding of truncated hemoglobin from Bacillus subtilis

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• 作者：Esther Fern ; ez ; Jonas T. Larsson ; Kirsty J. McLean ; Andrew W. Munro ; Lo Gorton ; Claes von Wachenfeldt ; Elena E. Ferapontova
• 关键词：Heme proteins ; Electron transfer ; Bacillus subtilis truncated hemoglobin ; Bioelectrocatalysis ; Ligand binding
• 刊名：Electrochimica Acta
• 出版年：1 November, 2013
• 年：2013
• 卷：110
• 期：Complete
• 页码：86-93
• 全文大小：1443 K

文摘

The truncated hemoglobin from Bacillus subtilis (trHb-Bs) possesses a surprisingly high affinity for oxygen and resistance to (auto)oxidation; its physiological role in the bacterium is not understood and may be connected with its very special redox and ligand binding reactions. Electron transfer reactions of trHb-Bs were electrochemically studied in solution and at graphite electrodes. Spectrophotometrical potentiometric titration and direct electrochemical measurements gave a heme iron redox potential of 鈭?03 卤 4 mV and 鈭?08 卤 2 mV vs. NHE, at pH 7, respectively. The redox potential of the heme in trHb-Bs shifted 鈭?9 mV per pH unit at pH higher than 7, consistently with a 1e^{鈭?/sup>/1 H+ - transfer reaction. The heterogeneous rate constant k_s for a quasi-reversible 1e鈭?/sup> - 1H+ - transfer reaction between graphite and trHb-Bs was 10.1 卤 2.3 s鈭?. Upon reversible cyanide binding the k_s doubled, while the redox potential of heme shifted 21 mV negatively, presumably reflecting changes in redox activity and in vivo signaling functions of trHb-Bs associated with ligand binding. Bioelectrocatalytic reduction of O₂ catalyzed by trHb-Bs was one of the most efficient hitherto reported for Hbs, with an apparent catalytic rate constant, k_cat, of 56 卤 6 s鈭?. The results obtained are of particular interest for applications of trHb in environmental biosensing and toxicity screening.}