Response of the NAD(P)H-oxidising flavohaemoglobin (Hmp) to prolonged oxidative stress and implications for its physiological role in Escherichia coli.
The Escherichia coli flavohaemoglobin (Hmp) has a globin-like N-terminal domain and a ferredoxin-NADP-reductase-like C-terminal domain. We show here that purified Hmp oxidises both NADH and NADPH with Km values of 1.8 and 19.6 microM, respectively. Prolonged incubation of a hmp-lacZ fusion strain with the redox cycling agent paraquat resulted in a 28-fold induction of hmp gene expression, nearly 3-fold higher than after short periods of exposure. A strain overproducing Hmp was significantly more sensitive to paraquat than was the wild-type strain but, in vitro, purified Hmp was not an effective NADPH-paraquat diaphorase. Prolonged incubation of a wild-type strain with paraquat increased intracellular Hmp to spectrally detectable levels.
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
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Anjum
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Ioannidis
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Poole
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D004093:Dihydropteridine Reductase; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006420:Hemeproteins / Q000235:genetics* / Q000378:metabolism*; D007763:Lac Operon; D009243:NAD / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*; D010269:Paraquat / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D011993:Recombinant Fusion Proteins; D009243:NAD; D009249:NADP; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases; D010269:Paraquat