Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

1. In respiratory nitrate reductase I of Klebsiella aerogenes, 0.24 atom of molybdenum, eight iron-sulfur groups and four tightly bound, non-heme iron atoms per molecule of enzyme (Mr 260 000) are found. 2. EPR spectra at 83 degrees K of oxidized and reduced nitrate reductase I show complex lines at g = 2.02 and g = 1.98, which are more intense in the reduced than in the oxidized enzyme. The resonances, the shape and intensity of which are rather temperature insensitive, are attributed to two species of paramagnetic molybdenum. In dithionite-reduced enzyme all these lines are saturated at the same microwave power of 15 mW. This is not the case in oxidized enzyme, where the resonance at g = 2.02 is hard to saturate. Addition of nitrate to dithionite-reduced reductase I decreases the intensity of the EPR lines to about that of oxidized enzyme. The participation of molybdenum in the electron transfer process has been discussed. 3. At 18 degrees K the oxidized enzyme exhibits an axial-symmetrical signal with g parallel = 2.10 and g = 2.03, and a signal with unknown symmetry at g = 2.015. Upon reduction by dithionite, a ferredoxin type of signal is observed with g values at 2.05, 1.95 and 1.88, while the g = 2.015 signal disappears. Reoxidation by nitrate causes a concomitant disappearance of the ferredoxin type of signal and reappearance of the g = 2.015 signal; hence iron-sulfur centres participate in the transfer of electrons to nitrate. 4. Nitrate reductase II, containing only two (Mr 117 000 and 57 000) of the three subunits found in nitrate reductase I and lacking the tightly bound iron, does not exhibit the axial-symmetrical signal (g = 2.10 and 2.03). Thus, it suggested that this signal in nitrate reductase I stems from an iron centre in the low-molecular weight subunit (Mr 52 000). 5. Inhibition studies confirm the participation of metals in the transfer of electrons from reduced benzylviologen to nitrate and show that the binding sites for these substrates are different.
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PMID:Characterization of the respiratory nitrate reductase of Klebsiella aerogenes as a molybdenum-containing iron-sulfur enzyme. 17 Sep 83

The ability of the oxidized and singly reduced species of several bipyridylium cations to cross the cytoplasmic membrane of Escherichia coli was studied to locate the sites of reaction of the dyes with anaerobic respiratory enzymes. Benzyl Viologen radical crossed the membrane rapidly, whereas the oxidized species did not. The oxidized or radical species of Methyl Viologen, Morfamquat or Diquat did not rapidly cross the membrane. It was also shown that the dithionite anion does not cross the cytoplasmic membrane of E. coli. Diquat radical donates electrons to the nitrate reductase pathway at the periplasmic aspect of the membrane, whereas Benzyl Viologen radical reacted directly with nitrate reductase itself (EC 1.7.99.4) at the cytoplasmic aspect of the membrane. Thus the pathway of electron transfer in the nitrate reductase pathway is transmembranous. Formate hydrogenlyase (EC 1.2.1.2) and an uncharacterized nitrite reductase activity react with bipyridylium dyes at the periplasmic aspect of the membrane. Fumarate reductase (succinate dehydrogenase; EC 1.3.99.1) reacts with bipyridylium radicals, and formate dehydrogenase (cytochrome) (EC 1.2.2.1) with ferricyanide, at the cytoplasmic aspect of the membrane. The differing charge and membrane permeation of oxidized and radical species of bipyridylium dyes greatly complicate their use as potentiometric mediators in suspensions of cells or membrane vesicles.
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PMID:Sites and specificity of the reaction of bipyridylium compounds with anaerobic respiratory enzymes of Escherichia coli. Effects of permeability barriers imposed by the cytoplasmic membrane. 32 10

The maize root has two main proteinase and carboxypeptidase components. Proteinase I and carboxypeptidase I, which predominate in older plants, appear to have a serine group at their active sites and have been estimated to have molecular weights of approximately 54000 and 77000 respectively. Proteinase I, which has been purified up to 500-fold, degrades haemoglobin and azocasein with maximum activity at pH 4 and 9--10 respectively, while on maize root protein it gives most hydrolysis in the neutral pH range. The main portion of the nitrate-reductase-inactivating activity in the maize root extract is due to proteinase I. Carboxypeptidase I, like several other plant carboxypeptidases such as carboxypeptidase C which have now (IUB Recommendations 1978) been classified as serine carboxypeptidases (EC 3.4.16.1), has maximum activity around pH 5 and has esterase activity. A second group of proteases, proteinase II and carboxypeptidase II, separated from the above on carboxymethyl-cellulose, were shown to have different molecular weight properties and be equally sensitive to serine and thiol group inhibitors. Proteinase II degrades haemoglobin, but not azocasein and does not mediate nitrate reductase inactivation. Associated with this second group of proteases was a macromolecular component which inactivated nitrate reductase but, unlike the action of proteinase I, was not inhibited by phenylmethylsulphonyl fluoride or casein. It was inhibited by metal chelating agents which were without effect on nitrate reductase inactivation due to proteinase I.
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PMID:Isolation and characterisation of peptide hydrolases from the maize root. 39 8

Nitrate reductase A has been solubilized from purified cytoplasmic membranes by extraction with tert-amyl alcohol. The resulting aqueous solution contained monomeric reductase which polymerized slowly to dimers and tetramers with sedimentation coefficients of respectively 10.5, 16 and 23 Svedbergunits. The polymerization could be stopped to some extent by addition of a small amount of Triton X-100. These distinct entities of nitrate reductase A were separable on electro-focusing, DEAE-column chromatography and polyacrylamide gel electrophoresis, and have been proved to consist of similar subunits with molecular weights of 104000, 63000, and 56000 daltons. The molecular weights of monomeric nitrate reductase A was found to be about 240000 daltons. Chlorate reductase C has been solubilized by a similar procedure, resulting in only monomeric enzyme. Chlorate reductase C exhibited a sedimentation coefficient of 7.7 Svedbergunits, an isoelectric point of pH = 4.55 and a molecular weight of approx. 180000 daltons. It was found to consist of three subunits with molecular weights of 75000, 63000 and 56000 daltons. The latter two subunits are most probably common in nitrate reductase A and chlorate reductase C.
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PMID:Characterization of purified nitrate reductase A and chlorate reductase C from Proteus mirabilis. 79 37

Three genotypically different chlorate resistant mutants, chl I, chl II and chl III, appeared to lack completely nitrate reductase A, chlorate reductase C and tetrathionate reductase activity. Fumarate reductase is only partially affected in chl I and chl III and unaffected in chl II. Formate dehydrogenase is only partially diminished in chl II, hydrogenase is diminished in chl I and chl II and completely absent in chl III. Subunits of nitrate reductase A, chlorate reductase C and tetrathionate reductase have been identified in protein profiles of purified cytoplasmic membranes from the wild type and the three mutant strains, grown under various conditions. Only the presence and absence of the largest subunits of these enzymes appeared to be correlated with their repression and derepression in the wild type membranes. On the cytoplasmic membranes of the chl I and chl III mutants these subunits lack for the greater part. In the chl II mutant, however, these subunits are inserted in the membrane all together after anaerobic growth with or without nitrate. A model for the repression/derepression mechanism for the reductases has been proposed. It includes repression by cytochrome b components, whereas the redox-state of the nitrate reductase A molecule itself is also involved in its derepression under anaerobic conditions.
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PMID:The correlation between the protein composition of cytoplasmic membranes and the formation of nitrate reductase A, chlorate reductase C and tetrathionate reductase in Proteus mirabilis wild type and some cholate resistant mutants. 79 38

Denitrification in a thermophile isolated on nitrite containing-medium (5 g/l) was studied by means of Warburg respirometry and gas chromatography. This strain seems to denitrify nitrite more rapidly than nitrate. Extracts of cells grown anaerobically on nitrate have dissimilatory nitrate reductase (type A); extracts of cells grown aerobically without nitrate have raised levels of the two types of nitrate reductase A and B. The optimal temperature for enzyme A activity is 60 degrees C. Nitrite reductase activity was measured using yeast extract as electron donor. For nitric oxide reductase activity, yeast extract is as efficient an electron donor as sodium lactate. Nitrous oxide reductase activity was found only in the 4 000 g supernatant showing the particulate nature of the enzyme. A mixture of FAD, FMN and NADH served as electron donor. Using acetylene as an inhibitor of nitrous oxide reduction in both whole cells and extracts, we showed that this gas is an intermediate compound in the reduction of NO to N2.
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PMID:[Denitrification in a sporulating thermophilic bacterium]. 91 Nov 9

The levels of nitrate reductase, nitrite reductase, and acid proteinase were compared in the primary leaves of 8-day-old wheat seedlings of Chinese Spring, Hope, and the 21 disomic substitution lines of Hope in Chinese Spring. Two chromosomes, 7B and 7D, were considered to contain genes controlling the level of nitrate reductase. Substitution of Hope chromosome 7B caused a highly significant increase in the in vitro stability of nitrate reductase. Nitrite reductase appeared to be controlled by two major genes, located on chromosomes 4D and 7D, and two minor genes, located on chromosomes 3D and 5A. In the case of acid proteinase, substitution of chromosome 1D caused a significant reduction in enzyme activity.
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PMID:Identification of wheat (Triticum aestivum L.) chromosomes with genes controlling the level of nitrate reductase, nitrite reductase, and acid proteinase using the Chinese Spring-Hope substitution lines. 101 25

Respiratory nitrate reductase with lactate as a hydrogen donor has been studied in cells and spheroplast preparations of wild type and heme-deficienct mutants of Staphylococcus aureus. The activity is rapidly induced when suspensions of aerobically grown cells are incubated without aeration in a complete medium with nitrate. In ruptured spheroplast preparations, the activity with lactate as the donor is located in the membrane fraction, whereas at least 50% of the activity assayed with reduced benzyl viologen is in the cytoplasm. The reductase is inhibited by azide and cyanide, and the lactate-linked system is also sensitive to oxamate, 2-heptyl-4-hydroxyquinoline-N-oxide, dicoumarol, and p-chloromercuribenzoate. An inactive form of the reductase is apparently made during induction with tungstate; this can be activated by subsequent incubation with molybdate in the presence of chloramphenicol. Nitrate reductase activity with reduced benzyl viologen as the donor is induced in suspensions of heme-deficient mutants in the presence or absence of heme. The proportion of cytoplasmic activity is increased in the absence of heme. The staphylococcal nitrate reductase has many of the characteristics commonly associated with the respiratory enzyme in other organisms, but the apparent predominance of cytoplasmic activity is unusual.
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PMID:Nitrate reductase system in Staphylococcus aureus wild type and mutants. 114 Nov 99

Investigations of human saliva reductase activity report the enzyme inactivation in 5-min heating at 50 degrees C, its maximal activity in neutral medium, reduced specific activity in the saliva dilution. Routine centrifugation inactivated nitrate reductase in supernatant, its activity in the precipitate hardly reached 10%. Combination of supernatant with precipitate recovered the baseline activity completely. Nitrates reduction into nitrites requires donor electrons. The latter are suggested to be present in the supernatant. Dehydrogenases substrates (lactate, pyruvate, malate, etc.) may act as donor electrons for nitrate reductase reaction. The addition of lithium lactate instead of supernatant to the precipitate partially recovered nitrate reductase activity. Biological role of salivary nitrate reductase is considered.
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PMID:[The nitrate reductase activity of human saliva]. 129 70

The redox properties of the iron-sulfur centers of the two nitrate reductases from Escherichia coli have been investigated by EPR spectroscopy. A detailed study of nitrate reductase A performed in the range +200 mV to -500 mV shows that the four iron-sulfur centers of the enzyme belong to two classes with markedly different redox potentials. The high-potential group comprises a [3Fe-4S] and a [4Fe-4S] cluster whose midpoint potentials are +60 mV and +80 mV, respectively. Although these centers are magnetically isolated, they are coupled by a significant anticooperative redox interaction of about 50 mV. The [4Fe-4S]1+ center occurs in two different conformations as shown by its composite EPR spectrum. The low-potential group contains two [4Fe-4S] clusters with more typical redox potentials (-200 mV and -400 mV). In the fully reduced state, the three [4Fe-4S]1+ centers are magnetically coupled, leading to a broad featureless spectrum. The redox behaviour of the high-pH EPR signal given by the molybdenum cofactor was also studied. The iron-sulfur centers of the second nitrate reductase of E. coli, nitrate reductase Z, exhibit essentially the same characteristics than those of nitrate reductase A, except that the midpoint potentials of the high-potential centers appear negatively shifted by about 100 mV. From the comparison between the redox centers of nitrate reductase and of dimethylsulfoxide reductase, a correspondence between the high-potential iron-sulfur clusters of the two enzymes can be proposed.
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PMID:EPR and redox characterization of iron-sulfur centers in nitrate reductases A and Z from Escherichia coli. Evidence for a high-potential and a low-potential class and their relevance in the electron-transfer mechanism. 132 Oct 49


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