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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Study of kinetics of nitrate or nitrite disappearance in soils incubating with atmosphere with or without acetylene, shows that the presence of this gas increases the rate of nitrate or nitrite reduction, and therefore very probably the denitrification process. The decrease of inhibitory effect on N2O-reductase after incubation during 15 days appears to be due to a great extent at a biological transformation of this gas with a consecutive increase of CO2 production. On the other hand, acetylene does not seem to affect perceptibly nitrate immobilisation.
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PMID:[Quantitative study of biological denitrification in soils with the aid of acetylene. II.--Evolution of inhibitory effect of acetylene on N2O-reductase; influence of acetylene on denitrification rate and on nitrate immobilisation (author's transl)]. 677 91

The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3-, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3- was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3- at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar Km values, 7 muM. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium.
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PMID:Assimilatory nitrate uptake in Pseudomonas fluorescens studied using nitrogen-13. 678 47

Six mutant strains (301, 102, 203, 104, 305, and 307) affected in their nitrate assimilation capability and their corresponding parental wild-type strains (6145c and 21gr) from Chlamydomonas reinhardii have been studied on different nitrogen sources with respect to NAD(P)H-nitrate reductase and its associated activities (NAD(P)H-cytochrome c reductase and reduced benzyl viologen-nitrate reductase) and to nitrite reductase activity. The mutant strains lack NAD(P)H-nitrate reductase activity in all the nitrogen sources. Mutants 301, 102, 104, and 307 have only NAD(P)H-cytochrome c reductase activity whereas mutant 305 solely has reduced benzyl viologen-nitrate reductase activity. Both activities are repressible by ammonia but, in contrast to the nitrate reductase complex of wild-type strains, require neither nitrate nor nitrite for their induction. Moreover, the enzyme from mutant 305 is always obtained in active form whereas nitrate reductase from wild-types needs to be reactivated previously with ferricyanide to be fully detected. Wild-type strains and mutants 301, 102, 104, and 307, when properly induced, exhibit an NAD(P)H-cytochrome c reductase distinguishable electrophoretically from constitutive diaphorases as a rapidly migrating band. Nitrite reductase from wild-type and mutant strains is also repressible by ammonia and does not require nitrate or nitrite for its synthesis. These facts are explained in terms of a regulation of nitrate reductase synthesis by the enzyme itself.
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PMID:Regulation of the nitrate-reducing system enzymes in wild-type and mutant strains of Chlamydomonas reinhardii. 681 63

The use of eight rapid tests for the identification of 1307 strains of mycobacteria belonging to 18 species was evaluated. The standard niacin, nitrate-reductase and catalase tests were supplemented by new tests for the detection of beta glucosidase, urease, penicillinase, trehalase and cephalosporinase. This combination of eight rapid tests was not able to replace more conventional procedures but in some cases was of value in discriminating between closely related species.
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PMID:Evaluation of rapid tests for the identification of mycobacteria. 681 37

The N-nitroso-compounds and the bacteriological contamination of gastric juice could represent a risk factor for cancer of the stomach when the mucosal barrier is altered. In the unresected stomach and gastric stump, the hypo-achlorhydria and bilopancreatic reflux permit the development of bacterial flora and the production of N-nitroso-compounds in the presence of nitrite. A survey was performed on 71 patients: 15 normal controls, 31 with gastroduodenal disease (9 gastrites, 10 gastric ulcers, 10 duodenal ulcers, 7 neoplasias), 20 patients with gastric resection (8 BI, 12 BII), using an endoscopic-histopathologic control and a chemical-bacteriological analysis of the gastric juice. We studied the gastric juice for the following parameters: pH, concentration of nitrite, identification of bacterial type, count and nitrate-reductase activity. An inverse relationship was found between the concentration of nitrite and the hydrogen ion concentration. In the alkaline gastric juice, we identified aerobic bacteria with nitrate-reductase activity and anaerobic bacteria. The latter has the ability to transform biliary salts into carcinogenic and cocarcinogenic compounds and to catalyze the nitrosations. The chemicobacteriological characteristics of the gastric juice from gastric ulcers (Johnson type I), atrophic gastrites, and resected stomachs lead one to think that there is a risk of carcinogenesis brought about by the N-nitroso-compounds.
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PMID:Gastric juice nitrite and bacteria in gastroduodenal disease and resected stomach. 686 41

The preliminary characterisation of an unusual gram-negative bacillus isolated from genital ulcers in Swaziland is reported. Like Haemophilus ducreyi, it is an oxidase positive, nitrate-reductase-positive gram-negative rod that forms streptobacillary chains in some circumstances; it was therefore called the "ducreyi-like bacterium" (DLB). Distinguishing features of DLB are production of alpha-haemolysis on horse-blood agar, stimulation of growth by a microaerophilic atmosphere and by a factor produced by Staphylococcus aureus, a strongly positive porphyrin test, and a remarkable ability to undergo autolysis. DLB had a guanine + cytosine value of c. 50 mole% but it cannot be classified, even at the genus level, until more taxonomic data are obtained.
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PMID:Characterisation of an unusual bacterium isolated from genital ulcers. 698 73

The toxic action of nitrates and nitrites has often been summarized by methemoglobinemia and nitrosation of amines inducing carcinogenic effects; these two impacts are spectacular, but they hide varying more or less insidious actions recently studied and perceived. In the NO3/NO2 couple, it is accepted that especially nitrite ion lays down a toxicological problem, probably because of its particular chemical reactivity: nitrite ion, which is the base of nitrous acid HNO2 (pKa = 3.36) can react with many functional groups from dietary or endogenous origin; it is also a reducing agent, only oxidable by chemical oxidants or adequate enzyme systems; at the same time it is an oxidant for many reduced substrates. These different possibilities explain the chemical complexity of these compounds and almost their reactivity in biological various media with toxicological implications (modification of the redox state). In man, the presence of nitrates in the digestive tract may result in nitrite formation, because nitrate-reductase from bacterial or enterocyte origin; more particularly in stomach, nitrites are characterized by a great instability imputable to the low pH of gastric juice and to secreted factors which accelerate phenomena; at the same time, nitrates and nutrites exercise opposite effects on gastric secretion (volume, acidity, pepsin) and on gastric mucosal irrigation: while nitrates increase these different parameters, nitrites reduce secretory activity but correlations between secretion and irrigation show that nitrates induce a deep modification of hydric compartment whereas nitrites rather react through cellular anoxy. In intestine, nitrates and chiefly nitrites are very quickly absorbed by a passive mechanism and they are characterized by an extrahepatic cycle; nitrates and nitrites are also eliminated in large quantities by kidneys, and nitrates have a very high diuretic effect: these NO3- ions move Cl- ions, inducing a Na+ waste, a decrease in extracellular space and an alkalosis; this diuretic action of ionic origin is moreover increased by a rise in glomerular blood flow facilitating filtration; these compounds therefore present vasomotor effects, probably by an action on catecholamines whose metabolism is modified. Last, nitrates are suspected to be responsible for reproduction troubles, thyroid dysfunction, perturbances of vitamins availability and nutritional effects. Most of the impacts of nitrates and nitrites are now well known, but their cellular of molecular action is not clear, and as a result there is a suspicion in regard to these products very widely present in food.
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PMID:[Toxicologic and nutritional aspects of nitrates and nitrites]. 702 May 46

The existence of a nitrate-reductase operon in the tryptophane region was deduced from the effects of prophage insertion in each of chlI and chlC genes and from transposition of the Mu-mediated host DNA fragments of F-prime. This operon appears to be polarized from chlC to chlI and the gene order in the region is trp -- chlI -- chlC -- purB.
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PMID:Nitrate reductase and cytochrome bnitrate reductase structural genes as parts of the nitrate reductase operon. 702 29

Demolybdo nitrate reductase (also called cyt c reductase) of Chlorella vulgaris has been converted to active nitrate reductase by insertion of Mo from Na2MoO4 in vitro. A procedure is described which consistently gives about 0.3 unit of nitrate reductase from about 6 units of cyt c reductase, a yield of 30% of the maximum expected, if we calculate on a basis of a ratio of 6 to 1 for the cyt c reductase/nitrate reductase of purified normal enzyme. The demolybdoenzyme is incubated for 30 s at 31 degrees C with molybdate and reduced glutathione (GSH) at pH 4.8, and the pH is then raised to 7, and the incubation continued for 20 min. At the acid pH, there must be a partial denaturation or unfolding which permits Mo insertion, with a refolding to active enzyme at the higher pH. The GSH is not essential for activation, but in its absence the yield of active enzyme was about 50% lower. Experiments with labeled GSH showed that no GSH was incorporated into the protein during the activation procedure. Although the enzyme activity measurements suggested that only 30% of the enzyme was activated, measurements with 99Mo showed that there was one Mo incorporated per subunit weight of 90,000. The Km for nitrate of the activated nitrate reductase was identical with the Km for nitrate of the normal enzyme. On gradient centrifugation, activated nitrate reductase, cyt c reductase, and normal nitrate reductase all behaved identically.
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PMID:Molybdenum insertion in vitro in demolybdo nitrate reductase of Chlorella vulgaris. 719 75

1. A method is described for preparing spheroplasts from Paracoccus denitrificans that are substantially depleted of dissimilatory nitrate reductase (cytochrome cd) activity. Treatment of cells with lysozyme + EDTA together with a mild osmotic shock, followed by centrifugation, yielded a pellet of spheroplasts and a supernatant that contained d-type cytochrome. The spheroplasts were judged to have retained an intact plasma membrane on the basis that less than 1% of the activity of a cytoplasmic marker protein, malate dehydrogenase, was released from the spheroplasts. In addition to a low activity towards added nitrite, the suspension of spheroplasts accumulated the nitrite that was produced by respiratory chain-linked reduction of nitrate. It is concluded that nitrate reduction occurs at the periplasmic side of the plasma membrane irrespective of whether nitrite is generated by nitrate reduction or is added exogenously. 2. Further evidence for the integrity of the spheroplasts was that nitrate reduction was inhibited by O2, and that chlorate was reduced at a markedly lower rate than nitrate. These data are taken as evidence for an intact plasma membrane because it was shown that cells acquire the capability to reduce nitrate under aerobic conditions after addition of low amounts of Triton X-100 which, with the same titre, also overcame the permeability barrier to chlorate reduction by intact cells. The close relationship between the appearance of chlorate reduction and the loss of the inhibitory effect of O2 on nitrate reduction also suggests that the later feature of nitrate respiration is due to a control on the accessibility of nitrate to its reductase rather than on the flow of electrons to nitrate reductase.
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PMID:The location of dissimilatory nitrite reductase and the control of dissimilatory nitrate reductase by oxygen in Paracoccus denitrificans. 719 18


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