Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.12.7.2 (hydrogenase)
 3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Electron paramagnetic resonance spectroscopic investigation of the inhibition of the phosphoroclastic system of Clostridium sporogenes by nitrite. 217 68

Nitrite, NO, CO, and C2H2 inhibited O2-dependent H2 uptake (H3H oxidation) in denitrifying Azospirillum brasilense Sp7 grown anaerobically on N2O or NO3-. The apparent Ki values for inhibition of O2-dependent H2 uptake were 20 microM for NO2-, 0.4 microM for NO, 28 microM for CO, and 88 microM for C2H2. These inhibitors also affected methylene blue-dependent H2 uptake, presumably by acting directly on the hydrogenase. Nitrite and NO inhibited H2 uptake irreversibly, whereas inhibition due to CO was easily reversed by repeatedly evacuating and backfilling with N2. The C2H2 inhibition was not readily reversed, partly due to difficulty in removing the last traces of this gas from solution. The NO2- inhibition of malate-dependent respiration was readily reversed by repeatedly washing the cells, in contrast to the effect of NO2- on H2-dependent respiration. These results suggest that the low hydrogenase activities observed in NO3(-)-grown cultures of A. brasilense may be due to the irreversible inhibition of hydrogenase by NO2- and NO produced by NO3- reduction.
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PMID:Hydrogenase activity in Azospirillum brasilense is inhibited by nitrite, nitric oxide, carbon monoxide, and acetylene. 638 89

Nitrite is widely used by bacteria as an electron acceptor under anaerobic conditions. In respiratory nitrite ammonification an electrochemical proton potential across the membrane is generated by electron transport from a non-fermentable substrate like formate or H(2) to nitrite. The corresponding electron transport chain minimally comprises formate dehydrogenase or hydrogenase, a respiratory quinone and cytochrome c nitrite reductase. The catalytic subunit of the latter enzyme (NrfA) catalyzes nitrite reduction to ammonia without liberating intermediate products. This review focuses on recent progress that has been made in understanding the enzymology and bioenergetics of respiratory nitrite ammonification. High-resolution structures of NrfA proteins from different bacteria have been determined, and many nrf operons sequenced, leading to the prediction of electron transfer pathways from the quinone pool to NrfA. Furthermore, the coupled electron transport chain from formate to nitrite of Wolinella succinogenes has been reconstituted by incorporating the purified enzymes into liposomes. The NrfH protein of W. succinogenes, a tetraheme c-type cytochrome of the NapC/NirT family, forms a stable complex with NrfA in the membrane and serves in passing electrons from menaquinol to NrfA. Proteins similar to NrfH are predicted by open reading frames of several bacterial nrf gene clusters. In gamma-proteobacteria, however, NrfH is thought to be replaced by the nrfBCD gene products. The active site heme c group of NrfA proteins from different bacteria is covalently bound via the cysteine residues of a unique CXXCK motif. The lysine residue of this motif serves as an axial ligand to the heme iron thus replacing the conventional histidine residue. The attachment of the lysine-ligated heme group requires specialized proteins in W. succinogenes and Escherichia coli that are encoded by accessory nrf genes. The proteins predicted by these genes are unrelated in the two bacteria but similar to proteins of the respective conventional cytochrome c biogenesis systems.
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PMID:Enzymology and bioenergetics of respiratory nitrite ammonification. 1216 29