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

Esther Fernandez, Jonas T. Larsson, Kirsty J. McLean, Andrew W. Munro, Lo Gorton, Claes Von Wachenfeldt, Elena E. Ferapontova

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    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 -103 ± 4 mV and -108 ± 2 mV vs. NHE, at pH 7, respectively. The redox potential of the heme in trHb-Bs shifted -59 mV per pH unit at pH higher than 7, consistently with a 1e-/1 H+ - transfer reaction. The heterogeneous rate constant ks for a quasi-reversible 1e- - 1H+ - transfer reaction between graphite and trHb-Bs was 10.1 ± 2.3 s-1. Upon reversible cyanide binding the ks 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, kcat, of 56 ± 6 s-1. The results obtained are of particular interest for applications of trHb in environmental biosensing and toxicity screening. © 2013 Elsevier Ltd.
    Original languageEnglish
    Pages (from-to)86-93
    Number of pages7
    JournalElectrochimica Acta
    Publication statusPublished - 2013


    • Bacillus subtilis truncated hemoglobin
    • Bioelectrocatalysis
    • Electron transfer
    • Heme proteins
    • Ligand binding


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