Flavohemoglobin Hmp affords inducible protection for Escherichia coli respiration, catalyzed by cytochromes bo' or bd, from nitric oxide.
Respiration of Escherichia coli catalyzed either by cytochrome bo' or bd is sensitive to micromolar extracellular NO; extensive, transient inhibition of respiration increases as dissolved oxygen tension in the medium decreases. At low oxygen concentrations (25-33 microm), the duration of inhibition of respiration by 9 microm NO is increased by mutation of either oxidase. Respiration of an hmp mutant defective in flavohemoglobin (Hmp) synthesis is extremely NO-sensitive (I(50) about 0.8 microm); conversely, cells pre-grown with sodium nitroprusside or overexpressing plasmid-borne hmp(+) are insensitive to 60 microm NO and have elevated levels of immunologically detectable Hmp. Purified Hmp consumes O(2) at a rate that is instantaneously and extensively (>10-fold) stimulated by NO due to NO oxygenase activity but, in the absence of NO, Hmp does not contribute measurably to cell oxygen consumption. Cyanide binds to Hmp (K(d) 3 microm). Concentrations of KCN (100 microm) that do not significantly inhibit cell respiration markedly suppress the protection of respiration from NO afforded by Hmp and abolish NO oxygenase activity of purified Hmp. The results demonstrate the role of Hmp in protecting respiration from NO stress and are discussed in relation to the energy metabolism of E. coli in natural O(2)-depleted environments.
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom.
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Stevanin
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Ioannidis
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Mills
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Kim
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Hughes
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Poole
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D003486:Cyanides / Q000378:metabolism / Q000494:pharmacology; D003573:Cytochrome b Group; D003580:Cytochromes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004093:Dihydropteridine Reductase; D004305:Dose-Response Relationship, Drug; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D006420:Hemeproteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D009603:Nitroso Compounds / Q000494:pharmacology; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects*; D026422:S-Nitrosoglutathione; D013053:Spectrophotometry
D001426:Bacterial Proteins; D003486:Cyanides; D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D009603:Nitroso Compounds; D009599:Nitroprusside; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; C017168:cytochrome bo, E coli; D010088:Oxidoreductases; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli; D005978:Glutathione; D010100:Oxygen