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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)

A new crystalline reagent for nitrate reductase tests was compared with standard liquid reagents on 437 strains of mycobacteria. The results for isolates of Mycobacterium avium complex, Mycobacterium kansasii, Mycobacterium gordonae, Mycobacterium scrofulaceum, Mycobacterium fortuitum, and Mycobacterium chelonei agreed 100% with the expected results. Of the 177 Mycobacterium tuberculosis isolates, 4 were negative by the conventional method. Two of these four isolates were positive with the new reagent. Of the positive nitrate tests carried out with liquid reagents, 42% flashed instantly or faded in color; none of the tests carried out with the new crystalline reagent flashed or faded. A stronger color reaction was seen for 28% of the positive tests with the new reagent.
J Clin Microbiol 1983 Sep
PMID:An improved reagent for mycobacterial nitrate reductase tests. 668 34

The assimilatory NADPH-nitrate oxidoreductase (EC 1.6.6.3) from Aspergillus nidulans was purified by means of affinity chromatography and analyzed by agarose isoelectric focusing and two-dimensional electrophoresis. NADPH-nitrate reductase activity was not activated by oxidation with potassium ferricyanide and was irreversibly inhibited by acrylamide. Electrophoresis of nitrate reductase in 7% polyacrylamide gels resulted in rapid loss of enzyme activity. Isoelectric focusing of purified enzyme in agarose gels resulted in the homogeneous band that exhibited NADPH-nitrate reductase, NADPH-cytochrome c reductase and reduced methyl viologen-nitrate reductase activities, which corresponded to an isoelectric point of 6.12 +/- 0.05 at 22 degrees C. Two-dimensional electrophoresis of focused nitrate reductase on SDS-polyacrylanide gel slabs yielded a single subunit of 54000 molecular weight. Acid treatment of the enzyme and subsequent isoelectric focusing resulted in a protein with a strongly acidic isoelectric point and reduced methyl viologen-nitrate reductase activity. It released another protein with a strongly basic isoelectric point which was inactive. It is postulated that the overall association of flavoprotein protomers with both heme and cytochrome b1 components confers a small net negative charge upon the native heteromultimer and accounts for its slightly acidic isoelectric point.
Biochim Biophys Acta 1982 Sep 07
PMID:Isoelectric focusing and two-dimensional analysis of purified nitrate reductase from Aspergillus nidulans. 675 5

Several reports had concluded that nitrates were not efficacious when administered by the oral route, on the basis of experiments which had shown a rapid denitration by the liver enzyme glutathion-organic nitrate reductase. Recent data demonstrate the efficacy of nitrates on parameters measured at cardiac catheterisation and echocardiography on condition that adequate doses are used. Doses commonly used up to now are often inadequate. The demonstration in the blood, after oral administration of adequate doses, of concentration of non-metabolized nitrates which are of the same order as those obtained after sublingual administration of clinically efficacious doses, confirms the efficacy of nitrates administered by the oral route.
Nouv Presse Med 1980 Sep 25
PMID:[Are nitrate compounds effective when administered orally? Results of pharmacokinetic and hemodynamic studies]. 677 93

The reduction of nitrate by reduced nicotinamide-adenine dinucleotides, catalysed by extract of Candida utilis, exhibits an apparent high degree of stereospecificity for the 'B' methylene hydrogen atom of NADPH and mixed stereospecificity for the methylene hydrogen atoms of NADH. Purified nitrate reductase, on the other hand, exhibits 'A' stereospecificity for NADH and NADPH. The apparent switch of stereospecificity from the 'B' to the 'A' side of NADPH, which occurs after purification of the enzyme, is partly explained by the fact that in crude extracts nitrate is reduced completely to ammonia. Nitrite does not accumulate but is reduced to ammonia by nitrite dehydrogenase, which is 'B'-specific, so that up to 75% of hydrogen removed from NADPH during the reduction of nitrate could occur from the 'B' side. A further increase in the removal of hydrogen from the 'B' side of NADPH could be the kinetic isotope effect that is observed when ['A'-3H]NADPH is the reductant, the H--C bond being cleaved 2.3 times faster than the 3H--C bond. The mixed stereospecificity observed with NADH has been traced to an uncharacterized enzyme that catalyses a 'B'-specific exchange between NAD+ and NADH. This reaction is discussed in relation to the possibility that it may explain other cases of apparent mixed stereospecificity that have been reported.
Biochem J 1982 Sep 01
PMID:The stereospecificity of the reduction of nitrate by reduced nicotinamide-adenine dinucleotides catalysed by Candida utilis preparations. 689 Aug 12

Gamma-irradiation induced high levels of nitrate reductase activity (NADH:nitrate oxidoreductase, EC 1.6.6.1) in callus of Haworthia mirabilis Haworth. Subcultures of gamma-irradiated tissues showed autonomous growth on minimal medium. We were able to mimic the effects of gamma-irradiation by inducing nitrate reductase activity in unirradiated callus with exogenous auxin and kinetin. These results revealed that induction of nitrate reductase activity by gamma-irradiation is mediated through in vitro activation of hormone synthesis in callus cells.
Proc Natl Acad Sci U S A 1982 Sep
PMID:Gamma-irradiation activates biochemical systems: induction of nitrate reductase activity in plant callus. 695 74

Cell-free extracts of Proteus mirabilis were able to reconstitute NADPH-dependent assimilatory nitrate reductase in crude extracts of the Neurospora crassa mutant strain nit-1, lacking molybdenum cofactor. Molybdenum cofactor was formed in the cytoplasm of the bacterium even in the presence of oxygen during growth though under these conditions no molybdo enzymes are formed. As a consequence no cofactor could be released by acid treatment from membranes of cells growth aerobically. The amount of cofactor released from membranes of cells grown anaerobically under various conditions was proportional to the amount of molybdo enzymes formed. During growth in the presence of tungstate a cofactor, which lacks molybdenum, was found in the cytoplasm. For detection of this so-called demolybdo cofactor the presence of molybdate during reconstitution was essential. Moreover, the cytoplasmic cofactor pool in cells grown in the presence of tungstate appeared to be two to three times higher than in cells grown under similar conditions without tungstate. After anaerobic growth in the presence of tungstate, the inactive demolybdo reductases were shown to contain partly no cofactor and partly a demolybdo cofactor. The P. mirabilis chlorate resistant mutant S 556 did not contain molybdenum cofactor. In two other chl-mutants the cofactor activity was the same as in the wild type.
Arch Microbiol 1981 Sep
PMID:The influence of growth conditions on the synthesis of molybdenum cofactor in Proteins mirabilis. 703 Feb 54

I used a chlC-lac operon fusion to study regulatory mutations which affect nitrate reductase expression in Escherichia coli. A NarL- mutant apparently lacks a nitrate-specific positive regulatory component. Furthermore, an fnr (nirR) mutation prevented enzyme induction under any conditions. These data are consistent with a two-step, positive control model for nitrate reductase regulation.
J Bacteriol 1982 Sep
PMID:Requirement of Fnr and NarL functions for nitrate reductase expression in Escherichia coli K-12. 705 87

Gel chromatography experiments over a wide range of protein concentrations showed that Chlorella nitrate reductase is a nonassociating protein with a Stokes radius of 81 A. Sedimentation equilibrium of nitrate reductase in H2O-D2O solvents yielded a partial specific volume of 0.800 +/- 0.014 (n = 12) and a Mr = 360,000 +/- 25,000. No lipid was found associated with nitrate reductase. Cross-linking with the bifunctional reagent, dimethyl suberimidate, and subsequent separation of products by sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded four protein-staining bands in which the molecular weights of the cross-linked products were integral multiples of the monomeric molecular weight (90,000). Extensive cross-linking of the enzyme resulted in one principal protein-staining band of 360,000, corresponding to a tetramer. The cross-linked tetramer of nitrate reductase appeared to have identical physical properties as the native enzyme. The cross-linking pattern produced by reaction with dimethyl suberimidate suggested that nitrate reductase is an isologous tetramer which has at least two different types of bonding domains. Gel filtration, sedimentation equilibrium, and density gradient experiments at very low enzyme concentrations indicated that nitrate reductase dissociates to a species with a Stokes radius of 54 A, s20.w of 7.1, and Mr = approximately 200,000 at these low enzyme concentrations. No change in specific activity of the enzyme was observed over this concentration range. Treatment of nitrate reductase with trypsin or with cyanogen bromide yielded the number of peptides expected for identical subunits. From these results, it is concluded that Chlorella nitrate reductase is a homotetramer with dihedral symmetry ("dimer of dimers").
J Biol Chem 1982 Sep 10
PMID:Quaternary structure of assimilatory NADH:nitrate reductase from Chlorella. 720 4

Based on Lineweaver-Burk plots of the initial velocities, at different concentrations of NADH and nitrate, and product inhibition patterns, an Iso Ping Pong Bi Bi steady state kinetic mechanism is proposed for the spinach nitrate reductase. This mechanism incorporates the concept that the oxidized enzyme is present in two isomeric forms.
Rev Esp Fisiol 1980 Sep
PMID:Studies on the kinetic mechanism of nitrate reductase from spinach (Spinacea oleracea). 743 51

DNA sequencing of the region upstream from the Azotobacter vinelandii operon (modEABC) that contains genes for the molybdenum transport system revealed an open reading frame (modG) encoding a hypothetical 14-kDa protein. It consists of a tandem repeat of an approximately 65-amino-acid sequence that is homologous to Mop, a 7-kDa molybdopterin-binding protein of Clostridium pasteurianum. The tandem repeat is similar to the C-terminal half of the product of modE. The effects of mutations in the mod genes provide evidence for distinct high- and low-affinity Mo transport systems and for the involvement of the products of modE and modG in the processing of molybdate. modA, modB, and modC, which encode the component proteins of the high-affinity Mo transporter, are required for 99Mo accumulation and for the nitrate reductase activity of cells growing in medium with less than 10 microM Mo. The exchange of accumulated 99Mo with nonradioactive Mo depends on the presence of modA, which encodes the periplasmic molybdate-binding protein. 99Mo also exchanges with tungstate but not with vanadate or sulfate. modA, modB, and modC mutants exhibit nitrate reductase activity and 99Mo accumulation only when grown in more than 10 microM Mo, indicating that A. vinelandii also has a low-affinity Mo uptake system. The low-affinity system is not expressed in a modE mutant that synthesizes the high-affinity Mo transporter constitutively or in a spontaneous tungstate-tolerant mutant. Like the wild type, modG mutants only show nitrate reductase activity when grown in > 10 nM Mo. However, a modE modG double mutant exhibits maximal nitrate reductase activity at a 100-fold lower Mo concentration. This indicates that the products of both genes affect the supply of Mo but are not essential for nitrate reductase cofactor synthesis. However, nitrogenase-dependent growth in the presence or absence of Mo is severely impaired in the double mutant, indicating that the products of modE and modG may be involved in the early steps of nitrogenase cofactor biosynthesis in A. vinelandii.
J Bacteriol 1995 Sep
PMID:Mutational analysis of genes of the mod locus involved in molybdenum transport, homeostasis, and processing in Azotobacter vinelandii. 766 18


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