The bacterioferritin (BFR) of Escherichia coli takes up iron in the ferrous form and stores it within its central cavity as a hydrated ferric oxide mineral. The mechanism by which oxidation of iron (II) occurs in BFR is largely unknown, but previous studies indicated that there is ferroxidase activity associated with a site capable of forming a dinuclear-iron centre within each subunit [Le Brun, Wilson, Andrews, Harrison, Guest, Thomson and Moore (1993) FEBS Lett. 333, 197-202]. We now report site-directed mutagenesis experiments based on a putative dinuclear-metal-ion-binding site located within the BFR subunit. The data reveal that this dinuclear-iron centre is located at a site within the four-alpha-helical bundle of each subunit of BFR, thus identified as the ferroxidase centre of BFR. The metal-bound form of the centre bears a remarkable similarity to the dinuclear-iron sites of the hydroxylase subunit of methane mono-oxygenase and the R2 subunit of ribonucleotide reductase. Details of how the dinuclear centre of BFR is involved in the oxidation mechanism were investigated by studying the inhibition of iron (II) oxidation by zinc (II) ions. Data indicate that zinc (II) ions bind at the ferroxidase centre of apo-BFR in preference to iron (II), resulting in a dramatic reduction in the rate of oxidation. The mechanism of iron (II) oxidation is discussed in the light of this and previous work.
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December 1995
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Research Article|
December 01 1995
Identification of the ferroxidase centre of Escherichia coli bacterioferritin Available to Purchase
N E Le Brun;
N E Le Brun
*Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ
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S C Andrews;
S C Andrews
†The Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K.
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J R Guest;
J R Guest
†The Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K.
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P M Harrison;
P M Harrison
†The Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, U.K.
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G R Moore;
G R Moore
*Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ
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A J Thomson
A J Thomson
*Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1995 The Biochemical Society, London
1995
Biochem J (1995) 312 (2): 385–392.
Citation
N E Le Brun, S C Andrews, J R Guest, P M Harrison, G R Moore, A J Thomson; Identification of the ferroxidase centre of Escherichia coli bacterioferritin. Biochem J 1 December 1995; 312 (2): 385–392. doi: https://doi.org/10.1042/bj3120385
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