Escherichia coli flavohaemoglobin (Hmp) reduces cytochrome c and Fe(III)-hydroxamate K by electron transfer from NADH via FAD: sensitivity of oxidoreductase activity to haem-bound dioxygen.

Microbiology
Robert K PooleY Orii

Abstract

Escherichia coli flavohaemoglobin (Hmp) reduced purified mitochondrial cytochrome c aerobically in a reaction that was not substantially inhibited by superoxide dismutase, demonstrating that superoxide anion, the product of O2 reduction by Hmp, did not contribute markedly to cytochrome c reduction. Cytochrome c was reduced by Hmp even in the presence of 0.5 mM CO, when the haem B was locked in the ferrous, low-spin state, demonstrating that electron transfer to cytochrome c from NADH was via FAD, not haem. Hmp also reduced the ferrisiderophore complex Fe(III)-hydroxamate K from Rhizobium leguminosarum bv. viciae anaerobically in a CO-insensitive manner, but at low rates and with low affinity for this substrate. The NADH-cytochrome c oxidoreductase activity of Hmp was slightly sensitive to the binding and reduction of O2 at the haem. The Vmax of cytochrome c reduction fell from 7.1 s-1 in the presence of 0.5 mM CO to 5.0 s-1 in the presence of 100 microM O2, with no significant change in K(m) for cytochrome c (6.8 to 7.3 microM, respectively). O2 at near-micromolar concentrations diminished cytochrome c reduction to a similar extent as did 100 microM O2. Thus, Hmp acts as a reductase of broad specificity, apparently without invo...Continue Reading

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Citations

Nov 6, 2010·The Journal of Biological Chemistry·Marcus MiethkeMohamed A Marahiel
Sep 7, 2007·Microbiology and Molecular Biology Reviews : MMBR·Marcus Miethke, Mohamed A Marahiel
Sep 22, 2009·Canadian Journal of Microbiology·Taija S Koskenkorva-Frank, Pauli T Kallio
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Sep 8, 1998·Microbiology and Molecular Biology Reviews : MMBR·M K Berlyn

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