title: Electron paramagnetic resonance spectroscopic investigation of the inhibition of the phosphoroclastic system of Clostridium sporogenes by nitrite.
abstract: The proposal that nitrite exerts its inhibitory effect on anaerobic bacteria by direct interaction with the iron-sulphur proteins of the phosphoroclastic system was investigated. The effects of nitrate, nitrite with or without ascorbate, and nitric oxide on the growth of Clostridium sporogenes in liquid cultures at pH 7.4, on the rates of hydrogen production, and on the activities of the enzymes pyruvate-ferredoxin oxidoreductase and hydrogenase, and of ferredoxin were investigated. In agreement with previous studies, nitrate was the least effective inhibitor of cell growth, and nitric oxide the most effective. Nitrite reductase activity was very low in C. sporogenes, indicating that the presence of external reducing agents would be necessary for the reduction of nitrite to nitric oxide. Inhibition by nitrite was enhanced by ascorbate; 0.5 mM-nitrite with 10 mM-ascorbate stopped growth completely. In partially-purified preparations 4.1 mM-NaNO2 and equimolar ascorbate caused complete inactivation of hydrogenase activity but only partial (up to 78%) inactivation of pyruvate-ferredoxin oxidoreductase. This agreed with the loss of hydrogen production observed with nitrite in vivo. Inhibition occurred within 5 min, and was irreversible in each case. Electron paramagnetic resonance (EPR) spectroscopy showed that paramagnetic [Fe(NO)2(SR)2] species were formed during growth in the presence of nitrite, and were associated with cells. However, the intensity of these EPR signals did not correlate with the inhibition of cell growth. The [4Fe-4S] clusters in ferredoxin were shown by EPR spectroscopy to be resistant to treatment with 3.6 mM-NaNO2 and 3.6 mM-ascorbate. It is concluded that the effects of nitrite on pre-formed iron-sulphur proteins are not convincing as a basis for the lethal effects on bacterial cells.
authors.affiliation: Department of Biomolecular Sciences, King's College London, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Payne
authors.forename: L F
authors.initials: LF
authors.lastname: Woods
authors.forename: P
authors.initials: P
authors.lastname: Gibbs
authors.forename: R
authors.initials: R
authors.lastname: Cammack
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D003013:Clostridium / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005516:Food Microbiology; D005520:Food Preservatives / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000037:antagonists & inhibitors; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007658:Ketone Oxidoreductases / Q000037:antagonists & inhibitors; D009566:Nitrates / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology; D009572:Nitrite Reductases / Q000378:metabolism; D009573:Nitrites / Q000494:pharmacology*; D050743:Pyruvate Synthase
chemical_list: D005520:Food Preservatives; D007506:Iron-Sulfur Proteins; D009566:Nitrates; D009573:Nitrites; D009569:Nitric Oxide; D006859:Hydrogen; D006864:Hydrogenase; D007658:Ketone Oxidoreductases; D050743:Pyruvate Synthase; D009572:Nitrite Reductases; D001205:Ascorbic Acid