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:1.7.1.1 (nitrate reductase)
3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Escherichia coli trimethylamine N-oxide (TMAO) reductase I, the major enzyme among inducible TMAO reductases, was purified to homogeneity by an improved method including heat treatment, ammonium sulfate precipitation, and chromatographies on Bio-Gel A-1.5m, DEAE-cellulose, and Reactive blue-agarose. The molecular weight was estimated by gel filtration to be approximately 200,000. A single subunit peptide with a molecular weight of 95,000 was found by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This enzyme contained 1.96 atoms of molybdenum, 0.96 atoms of iron, 1.52 atoms of zinc, and less than 0.4 atoms of acid-labile sulfur per molecular weight of 200,000. The absorption spectrum of the enzyme showed a peak at 278 nm and a shoulder at 288 nm, but no characteristic absorption was found from 350 to 700 nm. A fluorescent derivative of molybdenum cofactor was found when the enzyme was boiled with iodine in acidic solution; its fluorescence spectra were almost the same as those of the form A derivative of molybdopterin found in sulfite oxidase. The molybdenum cofactor released from heated TMAO reductase I reconstituted nitrate reductase in the extracts of Neurospora crassa mutant strain nit-1 lacking molybdenum cofactor. Thus, TMAO reductase I contains molybdopterin, which is a common constituent of some molybdenum-containing enzymes. Some kinetic properties were also determined.
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PMID:Further characterization of trimethylamine N-oxide reductase from Escherichia coli, a molybdoprotein. 352 39

In vivo labelling and in vitro translation studies were used to study the regulation of the synthesis of nitrate reductase in the yeast Candida nitratophila. These studies showed that synthesis of the enzyme subunit took place when ammonium-grown cells were nitrogen-starved and this was stimulated by subsequent addition of nitrate. Ammonium-grown cultures did not contain mRNA that could be translated into the nitrate reductase subunit in an in vitro system. Nitrate reductase mRNA could be extracted from nitrogen-starved and nitrate cultures. Synthesis of the enzyme is apparently controlled at the level of transcription in this yeast.
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PMID:Evidence for the transcriptional control of nitrate reductase in Candida nitratophila from in vitro translation studies. 356 70

Four detergents (octyl glucoside, zwittergent, Triton X-100, and Nonidet P-40) were examined with regard to their efficiency in solubilizing and retaining the activity of the nitrate reductase of Bacillus stearothermophilus. At a concentration of between 0.4 and 0.6%, the non-ionic detergent octyl glucoside solubilized only 64% of the membrane proteins. However, about 100% of the nitrate reductase activity was recovered in the soluble fraction. In contrast, the zwitterionic detergent 3-(alkyldimethylammonio)-1-propanesulphonate (3-16) solubilized 100% of the membrane proteins, but only 77% of the nitrate reductase activity was recovered. Two other non-ionic detergents, Triton X-100 and Nonidet P-40 also solubilized 100% of the membrane proteins, but there was a dramatic increase in total enzyme activity following solubilization. The enzyme activity was not stable in any of the four detergents for more than 2 days. Nevertheless, octyl glucoside was preferred because of the additional advantage of ammonium sulphate fractionation.
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PMID:Detergent solubilization of the respiratory nitrate reductase of Bacillus stearothermophilus. 378 23

Twenty L-amino acids and several inorganic compounds were tested individually, as a sole nitrogen source, for ability to support the growth of Mycobacterium avium LM1 serovar 1. Of the amino acids tested, only L-glutamine provided nutritional support comparable to that of ammonium chloride at 1 mM. With either 1 mM potassium nitrate or nitrite substituted for ammonium chloride, similar numbers of CFU were produced. M. avium cells were grown in potassium nitrate or nitrite concentrations of 0.25, 0.5, 1.0, and 2.0 mM, and the medium was assayed for remaining nitrogen compound at several times during growth. Rates of utilization were of first-order kinetics, with nitrite removed more rapidly than nitrate. The rates were approximately 10 times as rapid at 0.25 mM than at 2 mM for either nitrogen source. Nine clinical isolates that included M. avium serovars 1, 4, and 8 and Mycobacterium scrofulaceum serovar 43 were tested for rate of utilization of ammonia, nitrate, or nitrite. Ammonia and nitrite were utilized with first-order kinetics by all strains. Nitrate utilization occurred but was not at the same level for all strains. Clinical tests indicate that M. avium is negative for nitrate reductase; this is because of the rapid reduction of nitrite produced from nitrate.
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PMID:Utilization of nitrate or nitrite as single nitrogen source by Mycobacterium avium. 381 23

l-Glutamate uptake, thiourea uptake, and methylammonium uptake and the intracellular ammonium concentration were measured in wild-type and mutant cells of Aspergillus nidulans held in various concentrations of ammonium and urea. The levels of l-glutamate uptake, thiourea uptake, nitrate reductase, and hypoxanthine dehydrogenase activity are determined by the extracellular ammonium concentration. The level of methylammonium uptake is determined by the intracellular ammonium concentration. The uptake and enzyme characteristics of the ammonium-derepressed mutants, meaA8, meaB6, DER3, amrA1, xprD1, and gdhA1, are described. The gdhA mutants lack normal nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase (NADP-GDH) activity and are derepressed with respect to both external and internal ammonium. The other mutant classes are derepressed only with respect to external ammonium. The mutants meaA8, DER3, amrA1, and xprD1 have low levels of one or more of the l-glutamate, thiourea, and methylammonium uptake systems. A model for ammonium regulation in A. nidulans is put forward which suggests: (i) NADP-GDH located in the cell membrane complexes with extracellular ammonium. This first regulatory complex determines the level of l-glutamate uptake, thiourea uptake, nitrate reductase, and xanthine dehydrogenase by repression or inhibition, or both. (ii) NADP-GDH also complexes with intracellular ammonium. This second and different form of regulatory complex determines the level of methylammonium uptake by repression or inhibition, or both.
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PMID:Ammonium regulation in Aspergillus nidulans. 414 65

A technique employing cycloheximide and actinomycin D has been used for the separation of transcription and translation during the induction of nitrate reductase in Neurospora crassa. Nitrate reductase is found to be synthesized in low efficiency when nitrate is not provided during both transcription and translation. Nitrate reductase synthesis is enhanced by nitrate. Nitrate is found to induce nitrate reductase by enhancing the increase of the capacity to synthesize nitrate reductase, and ammonia is found to repress nitrate reductase, by inhibiting the induced increase of the capacity to make the enzyme, or by making it unstable in vivo, or both. The effect of ammonia is partially reversed by nitrate. The addition of ammonium tartrate or the removal of nitrate during translation of the induced capacity to synthesize nitrate reductase is found to result in the inactivation of nitrate reductase in vivo. A low level of nitrate in the medium is found to be sufficient for enhancing the induced increase of the capacity to synthesize nitrate reductase, but a higher level of nitrate is required to stabilize the enzyme after its formation. The induced capacity to synthesize nitrate reductase is relatively stable in the presence or absence of nitrate, but not in the presence of ammonia.
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PMID:Regulation of nitrate reductase in Neurospora crassa: regulation of transcription and translation. 425 76

1. In Aspergillus nidulans nitrate and nitrite induce nitrate reductase, nitrite reductase and hydroxylamine reductase, and ammonium represses the three enzymes. 2. Nitrate reductase can donate electrons to a wide variety of acceptors in addition to nitrate. These artificial acceptors include benzyl viologen, 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride, cytochrome c and potassium ferricyanide. Similarly nitrite reductase and hydroxylamine reductase (which are possibly a single enzyme in A. nidulans) can donate electrons to these same artificial acceptors in addition to the substrates nitrite and hydroxylamine. 3. Nitrate reductase can accept electrons from reduced benzyl viologen in place of the natural donor NADPH. The NADPH-nitrate-reductase activity is about twice that of reduced benzyl viologen-nitrate reductase under comparable conditions. 4. Mutants at six gene loci are known that cannot utilize nitrate and lack nitrate-reductase activity. Most mutants in these loci are constitutive for nitrite reductase, hydroxylamine reductase and all the nitrate-induced NADPH-diaphorase activities. It is argued that mutants that lack nitrate-reductase activity are constitutive for the enzymes of the nitrate-reduction pathway because the functional nitrate-reductase molecule is a component of the regulatory system of the pathway. 5. Mutants are known at two gene loci, niiA and niiB, that cannot utilize nitrite and lack nitrite-reductase and hydroxylamine-reductase activities. 6. Mutants at the niiA locus possess inducible nitrate reductase and lack nitrite-reductase and hydroxylamine-reductase activities. It is suggested that a single enzyme protein is responsible for the reduction of nitrite to ammonium in A. nidulans and that the niiA locus is the structural gene for this enzyme. 7. Mutants at the niiB locus lack nitrate-reductase, nitrite-reductase and hydroxylamine-reductase activities. It is argued that the niiB gene is a regulator gene whose product is necessary for the induction of the nitrate-utilization pathway. The niiB mutants either lack or produce an incorrect product and consequently cannot be induced. 8. Mutants at the niiribo locus cannot utilize nitrate or nitrite unless provided with a flavine supplement. When grown in the absence of a flavine supplement the activities of some of the nitrate-induced enzymes are subnormal. 9. The growth and enzyme characteristics of a total of 123 mutants involving nine different genes indicate that nitrate is reduced to ammonium. Only two possible structural genes for enzymes concerned with nitrate utilization are known. This suggests that only two enzymes, one for the reduction of nitrate to nitrite, the other for the reduction of nitrite to ammonium, are involved in this pathway.
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PMID:Genetic and biochemical studies of nitrate reduction in Aspergillus nidulans. 438 27

Nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-nitrate reductase and its related enzyme activities, NADPH-cytochrome c reductase and reduced benzyl viologen-nitrate reductase, are all induced following the transfer of ammonia-grown wild-type Neurospora mycelia to nitrate medium. After nitrate reductase is induced to the maximal level, the addition of an ammonium salt to, or the removal of nitrate from, the cultures results in a rapid inactivation of nitrate reductase and its two partial component activities. This rapid inactivation is slowed down by the protein synthesis inhibitor, cycloheximide. Experiments on the mixing of extracts in vitro rule out the presence of an inhibitor of nitrate reductase in free form in extracts containing inactivated nitrate reductase. Ammonia does not inhibit the uptake of nitrate by the mycelia. Inactivation of nitrate reductase in vivo by ammonia depends on the concentration of the ammonium salt and is not reversed by increasing the nitrate concentration of the medium. The nitrate-inducible NADPH-cytochrome c reductase activity and reduced benzyl viologen-nitrate reductase activity respectively of the nitrate-nonutilizing mutants nit-1 and nit-3 are not inactivated in vivo by the addition of an ammonium salt or the withdrawal of nitrate. This finding suggests that the integrity of the nitrate reductase complex is required for the in vivo inactivation of nitrate reductase and its associated activities.
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PMID:Regulation of nitrate reductase in Neurospora crassa: stability in vivo. 440 13

Wild-type cells of Aspergillus nidulans synthesize a transport system which appears to be specific for l-glutamate and l-aspartate. The system is energy dependent and concentrates l-glutamate at least 60-fold. In cells grown in the presence of 1% sucrose, l-glutamate uptake activity is regulated by ammonium control, although it is not certain whether this is at the level of transcription or translation. Mutants that are insensitive to ammonium control of certain other unrelated systems, e.g., nitrate reductase, are also insensitive, except in the case of one class of ammonium-insensitive mutants, to ammonium control of l-glutamate transport. The activity of this transport system is specifically impaired in a mutant at the aauA locus. This mutation results in poor growth with l-glutamate or l-aspartate as the sole carbon or nitrogen source and is recessive in the heterozygous diploid aauA1/+ for transport and growth characteristics. The likelihood that the mutation results in a defect of the transport mechanism rather than abnormal ammonium control is discussed.
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PMID:Regulatory aspects of L-glutamate transport in Aspergillus nidulans. 460 30

During growth of Aspergillus nidulans in medium containing ammonium the specific activities of most enzymes involved in catabolism of nitrogen sources are low (ammonium repression). The gdhA10 lesion, which results in loss of nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase activity, has been shown to lead to partial relief of ammonium repression of three amidase enzymes as well as histidase. The areA102 lesion led to altered levels of these enzymes but did not greatly affect ammonium repression. The double mutant areA102,gdhA10 was almost completely insensitive to ammonium repression of two of the amidase enzymes and histidase. This suggests that an interaction between the areA and gdhA genes in determining responses to ammonium occurs. Growth of mycelium in medium containing l-glutamate has been found to result in lowered levels of all four enzymes, and this occurs in strains insensitive to ammonium repression. Very strong repression in all strains occurred during growth in medium containing l-glutamine. Relief of these repressive effects of glutamate and glutamine was blocked by cycloheximide. Glutamate and glutamine had similar effects on the production of extracellular protease activity, and growth on glutamine led to low levels of urate oxidase. In contrast to the above enzymes, nitrate reductase was insensitive to the effects of glutamine and glutamate, even though this enzyme is very sensitive to ammonium repression. Although other possibilities exist, it is suggested that there may be mechanisms of general control of nitrogen-catabolic enzymes other than ammonium repression.
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PMID:Effects of ammonium, L-glutamate, and L-glutamine on nitrogen catabolism in Aspergillus nidulans. 461 4


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