Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The assimilatory NADPH-nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.3) from Neurospora crassa is competitively inhibited by 3-aminopyridine adenine dinucleotide (AAD) and 3-aminopyridine adenine dinucleotide phosphate (AADP) which are structural analogs of NAD and NADP, respectively. The amino group of the pyridine ring of AAD(P) can react with nitrous acid to yield the diazonium derivative which may covalently bind at the NAD(P) site. As a result of covalent attachment, diazotized AAD(P) causes time-dependent irreversible inactivation of nitrate reductase. However, only the NADPH-dependent activities of the nitrate reductase, i.e. the overall NADPH-nitrate reductase and the NADPH-cytochrome c reductase activities, are inactivated. The reduced methyl viologen- and reduced FAD-nitrate reductase activities which do not utilize NADPH are not inhibited. This inactivation by diazotized AADP is prevented by 1 mM NADP. The inclusion of 1 muM FAD can also prevent inactivation, but the FAD effect differs from the NADP protection in that even after removal of the exogenous FAD by extensive dialysis or Sephadex G-25 filtration chromatography, the enzyme is still protected against inactivation. The FAD-generated protected form of nitrate reductase could again be inactivated if the enzyme was treated with NADPH, dialyzed to remove the NADPH, and then exposed to diazotized AADP. When NADP was substituted for NADPH in this experiment, the enzyme remained in the FAD-protected state. Difference spectra of the inactivated nitrate reductase demonstrated the presence of bound AADP, and titration of the sulfhydryl groups of the inactivated enzyme revealed that a loss of accessible sulfhydryls had occurred. The hypothesis generated by these experiments is that diazotized AADP binds at the NADPH site on nitrate reductase and reacts with a functional sulfhydryl at the site. FAD protects the enzyme against inactivation by modifying the sulfhydryl. Since NADPH reverses this protection, it appears the modifications occurring are oxidation-reduction reactions. On the basis of these results, the physiological electron flow in the nitrate reductase is postulated to be from NADPH via sulfhydryls to FAD and then the remainder of the electron carriers as follows: NADPH leads to -SH leads to FAD leads to cytochrome b-557 leads to Mo leads to NO-3.
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PMID:Reactions of the Neurospora crassa nitrate reductase with NAD(P) analogs. 1 30

During oxidation of nitrite, cells of Nitrobacter winogradskyi are shown to catalyze the active exchange of oxygen atoms between exogenous nitrate molecules (production of 15N16/18O3- during incubation of 14N16/18O3-, 15N16O3-, and 15N16O2- in H216O). Little, if any, exchange of oxygens between nitrate and water also occurs (production of 15N16/18O3- during incubation of 15N16O3- and 14N16O2- in H218O). 15N species of nitrate were assayed by 18O-isotope shift in 15N NMR. Taking into account the O-exchange reactions which occur during nitrite oxidation, H2O is seen to be the source of O in nitrate produced by oxidation of nitrite by N. winogradskyi. The data do not establish whether the nitrate-nitrate O exchange is catalyzed by nitrite oxidase (H2O + HNO2----HNO3 + 2H+ + 2e-) or nitrate reductase (HNO3 + 2H+ + 2e-----HNO2 + H2O) or both enzymes in consort. The nitrate-nitrate exchange reaction suggests the existence of an oxygen derivative of a H2O-utilizing oxidoreductase.
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PMID:Oxygen exchange between nitrate molecules during nitrite oxidation by Nitrobacter. 373 17

Endonuclease V (Endo V) of Escherichia coli participates in the excision repair of hypoxanthine and xanthine (deaminated adenine and guanine) in DNA. It thereby reduces the mutagenic effects of nitrous acid by attacking lesions caused by nitrosative deamination. Nitrosating agents may be produced endogenously when E. coli is grown in oxygen-poor cultures, during which nitrate and nitrite replace oxygen as preferred electron acceptors. In this study, the protective effect of Endo V was observed under such conditions. During micro-aerobic growth, an nfi (Endo V) mutation enhanced the frequency of nitrate- and nitrite-induced A:T-->G:C and G:C-->A:T transition mutations, which are consistent with a defect in the removal of DNA hypoxanthine and xanthine, respectively. Similar effects were observed in saturated, aerobic cultures but not in well-aerated, logarithmically growing ones. A narG (nitrate reductase) mutation blocked the mutagenesis of the nfi mutant by nitrate but not by nitrite. These results differed from those of previous studies in which cell suspensions generated an exogenous nitrosating agent from nitrite, but not from nitrate, in a reaction that was narG-dependent. Nitrate/nitrite metabolism is also known to generate endogenous alkylating agents through N-nitrosation. However, an nfi mutation did not appreciably enhance mutagenesis by N-methyl-N-nitrosourea, suggesting that the mutator effect of nfi is not due to a defect in alkylation repair. The overall results indicate that Endo V functions during normal growth by helping to repair nitrosatively deaminated bases in DNA, which are by-products of anaerobic nitrate/nitrite respiration.
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PMID:Endonuclease V of Escherichia coli prevents mutations from nitrosative deamination during nitrate/nitrite respiration. 1110 6

The present study shows that when freezing nitrite containing biological samples in the presence of sodium and phosphate, a process of tyrosine nitration and S-nitrosocysteine formation is observed. The underlying mechanism is obviously based on the already described pH decrease in sodium phosphate buffered solutions during the freezing process and probably involves nitrous acid as an intermediate. However, in pure potassium phosphate buffer freeze-artefacts were absent. The yield of 3-nitrotyrosine from albumin-bound or free tyrosine depends not only on the concentration of nitrite, tyrosine or protein, and sodium phosphate but also on the velocity of the freezing process. Nitrite and nitrate were quantified by the Griess/nitrate reductase assay. 3-nitrotyrosine formation was quantitatively measured by HPLC analysis with optical and electrochemical detection as well as qualitatively investigated by immunohistochemistry and slot blot analysis using 3-nitrotyrosine specific antibodies. The formation of S-nitrosocysteine was detected by S-nitrosothiol specific antibodies and quantified by a fluorometric assay. Irrespective of the mechanism and although the here presented results cannot be generalized, the data warrant caution for the analysis of nitration or nitros(yl)ation products following freezing of nitrite containing biological material.
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PMID:A new pitfall in detecting biological end products of nitric oxide-nitration, nitros(yl)ation and nitrite/nitrate artefacts during freezing. 1556 66

When Escherichia coli K-12 is grown anaerobically in medium containing tryptophan and sodium nitrate, it produces red compounds. The reaction requires functional genes for trytophanase (tnaA), a tryptophan permease (tnaB), and a nitrate reductase (narG), as well as a natural drop in the pH of the culture. Mass spectrometry revealed that the purified chromophores had mass/charge ratios that closely match those for indole red, indoxyl red, and an indole trimer. These compounds are known products of chemical reactions between indole and nitrous acid. They are derived from an initial reaction of 3-nitrosoindole with indole. Apparently, nitrite that is produced from the metabolic reduction of nitrate is converted in the acid medium to nitrous acid, which leads to the nitrosation of the indole that is generated by tryptophanase. An nfi (endonuclease V) mutant and a recA mutant were selectively killed during the period of chromophore production, and a uvrA strain displayed reduced growth. These effects depended on the addition of nitrate to the medium and on tryptophanase activity in the cells. Unexpectedly, the killing of a tnaA(+) nfi mutant was not accompanied by marked increases in mutation frequencies for several traits tested. The vulnerability of three DNA repair mutants indicates that a nitrosoindole or a derivative of a nitrosoindole produces lethal DNA damage.
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PMID:Production of 3-nitrosoindole derivatives by Escherichia coli during anaerobic growth. 1956 Nov 28