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)

Partially purified soluble rat liver guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] was activated by superoxide dismutase (superoxide: superoxide oxidoreductase, EC 1.15.1.1). This activation was prevented with KCN or glutathione, inhibitors of superoxide dismutase. Guanylate cyclase preparations formed superoxide ion. Activation by superoxide dismutase was further enhanced by the addition of nitrate reductase. Although guanylate cyclase activity was much greater with Mn2+ than with Mg2+ as sole cation cofactor, activation with superoxide dismutase was not observed when Mn2+ was included in incubations. Catalase also decreased the activation induced with superoxide dismutase. Thus, activation required the formation of both superoxide ion and H2O2 in incubations. Activation of guanylate cyclase could not be achieved by the addition of H2O2 alone. Scavengers of hydroxyl radicals prevented the activation. It is proposed that superoxide ion and hydrogen peroxide can lead to the formation of hydroxyl radicals that activate guanylate cyclase. This mechanism of activation can explain numerous observations of altered guanylate cyclase activity and cyclic GMP accumulation in tissues with oxidizing and reducing agents. This mechanism will also permit physiological regulation of guanylate cyclase and cyclic GMP formation when there is altered redox or free radical formation in tissues in response to hormones, other agents, and processes.
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PMID:Activation of guanylate cyclase by superoxide dismutase and hydroxyl radical: a physiological regulator of guanosine 3',5'-monophosphate formation. 2 77

The described bacterium was isolated by enrichment culture in peptone broth inoculated with garden soil, pasteurized and then put to incubate under N2O at 32 degrees. It is a Gram-negative rod, motile with peritrichous flagella, and producing oval spores without exosporium in swollen sporangia. However, cells have the thick walls, mesosomes and persistant septa characteristic of Gram-positive bacteria. It lacks fermentative activity, does not attack carbohydrates, has complex growth requirements, and will grow anaerobically only if one of the following electron acceptors is present: NO3, NO2, N2O, S4O6, and fumarate. Nitrate, nitrite, and nitrous oxide are denitrified with production of N2. The microorganism is mesophilic, gives a positive oxidase reaction, synthesizes a type of c cytochrome, and does not hydrolyse gelatin, starch nor "Tween 80". The following enzymes are present: nitrate reductase A, respiratory nitrite reductase, tetrathionate and fumarate reductases, L-glutamate dehydrogenase, and superoxide dismutase. The following enzymes are absent: thiosulfate reductase, urease, lecithinase, arginine dihydrolase, L-alanine dehydrogenase, phenylalanine desaminase, and catalase. The GC% of its DNA is 39. The bacterium described can be considered to be a new species. We propose the name Bacillus azotoformans n. sp.
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PMID:[A new, sporulating, denitrifying, mesophilic bacterium: Bacillus azotoformans N. SP. (author's transl)]. 102 Aug 72

Escherichia coli growing anaerobically respond to NO3- with a approximately 3-fold induction of active FeSOD and a approximately 5.5-fold induction of an inactive, but activatable form of MnSOD (pro-MnSOD). Paraquat, which mediates anaerobic electron flow to NO3-, increased the induction of pro-MnSOD to approximately 2.5-fold. Strains with defects in the SOD genes or which lacked nitrate reductase activity failed to accumulate active or pro-forms of SODs in response to NO3- +/- PQ++. Diamide caused anaerobic induction of active MnSOD and this effect was also observed in a glutathione-negative strain. These inductions required de novo synthesis of protein, even when cell content of pro-MnSOD had been elevated by exposure to NO3- +/- PQ++ prior to addition of diamide. These results indicate that oxidation of a cell component increases biosynthesis of the SOD gene product and this postulated oxidation can be caused by terminal electron acceptors, such as dioxygen or NO3-. In addition, it appears that insertion of the correct metal can be rate-limiting, leading to competition by other metals and to the accumulation of inactive, incorrectly substituted pro-forms. Metal insertion may be dependent upon the valence of the metal, which may be influenced, in turn, by the redox status of the cells. Diamide and redox active agents such as ferricyanide may thus allow anaerobic production of active MnSOD by favoring the production of a complexed form of Mn(III) which can compete favorably with other metal cations for the active site of nascent MnSOD.
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PMID:Anaerobic inductions of active forms of superoxide dismutases in Escherichia coli. 207 Oct 46

Escherichia coli growing anaerobically respond to NO3- with a 3-fold induction of the iron-containing superoxide dismutase. Mutants lacking nitrate reductase do not show this response. Anaerobically grown cells also contain an inactive form of the manganese-containing superoxide dismutase (MnSOD) which can be activated by addition of Mn(II) salts in the presence of acidic guanidinium chloride, followed by dialysis against neutral buffer. Direct addition of Mn(II) to a neutral solution of the inactive MnSOD does not impart activity. This inactive MnSOD thus behaves as would the apoenzyme or the enzyme bearing a metal other than Mn(II) at its active sites. Terminal electron acceptors, such as NO3- or trimethylamine N-oxide, increase the amount of inactive MnSOD produced by anaerobic E. coli. Paraquat, which is itself ineffective in this regard, markedly augments the effect of these terminal electron acceptors. It appears that flow of electrons to sinks such as NO3- or trimethylamine N-oxide, facilitated by paraquat, is sufficient to elicit biosynthesis of the MnSOD protein and that O2- is not needed for this process. Yet, oxygenation and concomitant O2- production do appear important for the insertion of manganese into the growing MnSOD polypeptide, possibly because O-2 oxidizes Mn(II) to Mn(III), and the latter is the valence state most effective in combining with the apoenzyme.
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PMID:Inductions of superoxide dismutases in Escherichia coli under anaerobic conditions. Accumulation of an inactive form of the manganese enzyme. 327 33

The tehAtehB operon from the Escherichia coli chromosome (32.3 min) mediates resistance to potassium tellurite (K2TeO3) when expressed on a multicopy plasmid such as pUC8 (pTWT100). An MIC of 128 micrograms ml-1 is observed when tehAtehB is expressed in a wild-type host and grown on rich media. In this study, the tehAtehB determinant was transformed into mutants deficient in electron transport processes and/or thiol redox coupling within E. coli. These mutants included ubi, nad, cys, nar, trx, grx, gsh and sod. MICs of tehAtehB transformed into these mutants ranged from 1-16 micrograms K2TeO3 ml-1 compared to 0.03-2 micrograms ml-1 for strains transformed with a control plasmid. The tellurite-resistance determinant locus kilA cloned from the IncP alpha plasmid RK2Ter (pDT1558) was also investigated in these strains. This tellurite-resistance determinant showed little or no dependency on the host genotype. The ability of tehAtehB to mediate resistance in wild-type hosts is limited to rich medium. Rich medium may provide a key unidentified cofactor required by TehATehB that is not provided under minimal conditions. Again, the ability of the kilA determinant to mediate tellurite resistance was independent of medium conditions. These data suggest that either a reducing environment or electron-reducing equivalents are required for tehAtehB to mediate high levels of resistance to potassium tellurite. Therefore, the two resistance determinants studied here possess two very different biochemical mechanisms of resistance. Our data also suggest a mechanism for endogenous resistance to tellurite which involves nitrate reductase, superoxide dismutase, and thiol redox processes.
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PMID:The tellurite-resistance determinants tehAtehB and klaAklaBtelB have different biochemical requirements. 857 7

Assimilatory NADH:nitrate reductase catalyzes the transfer of reducing equivalents from NADH to molecular oxygen. Initial rate studies performed under conditions of optimal pH (8.0) and constant ionic strength (mu = 0.2) revealed that the maximal rate of activity with molecular oxygen was 0.5% (0.44 mumol NADH consumed/min/nmol heme) with a Km for O2 of 586 microM. NADH:molecular oxygen reductase activity exhibited a pH optimum of 9.2, was inhibited by cyanide, and was unaffected by changes in ionic strength or the presence of phosphate ions. Spectroscopic studies indicated NADH:molecular oxygen reductase activity resulted in the production of the superoxide radical, detected as the formation of adrenochrome from epinephrine and by the formation of adrenochrome from epinephrine and by the reduction of nitroblue tetrazolium, both of which could be inhibited by the addition of superoxide dismutase and were unaffected by the addition of catalase. Direct observation of superoxide production using spin-trapping in combination with EPR spectroscopy resulted in the detection of the spin adduct 5.5-dimethyl-5-hydroxy-1-pyrrolidinyloxy (DMPO-OH). The formation of this spin adduct was abolished either in the absence of nitrate reductase, NADH, or DMPO or the the addition of superoxide dismutase or nitrate and was greatly reduced by the presence of cyanide. Inclusion of catalase or ethanol had no effect on the formation of the spin adduct. These results indicate that nitrate reductase can utilize molecular oxygen as an electron acceptor and that the product, O2.(-), is primarily generated via the Mopterin center.
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PMID:Superoxide production during reduction of molecular oxygen by assimilatory nitrate reductase. 861 Oct 27

Biochemical responses of Pinus massoniana, with and without the inoculation mycorrhizal fungus Pisolithus tinctorius at the root, to artificial acid rain (pH 2.0) and various Ca/Al ratios were investigated. Some enzymes associated with the nutritive metabolism, such as acid phosphatase, alkaline phosphatase, nitrate reductase, mannitol dehydrogenase and trehalase, in the roots, stems and leaves of plant were obviously inhibited by the artificial acid rain and Al. After treatment with pH 2.0 + Ca/Al (0/1 or 1/10) artificial acid rain, the protein content in the organs was decreased. However, the activities of superoxide dismutase (SOD) and peroxidase (POD) and glutathione (GSH) concentrations were induced. It demonstrated that acid rain and Al could induce oxygen radicals in plant. Compared with the treatments with lower pH or Al, respectively, the combination of lower pH and Al concentration was more toxic to P. massoniana. Al toxicity could be ameliorated by the addition of Ca and the amelioration was the most when the ratio was 1/1 among the various Ca/Al ratio. Infection with mycorrhizal fungus P. tinctorius at the root of P. massoniana increased the ability of the plant to resist the toxicity of artificial acid rain and Al stress.
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PMID:Biochemical responses of the mycorrhizae in Pinus massoniana to combined effects of Al, Ca and low pH. 1066 22

Tobacco seedlings were inoculated with VA mycorrhizal fungi in natural soil. The results showed that compared with the control, the contents of nitrogen, phosphorus, potassium and chlorophyll, nitrate reductase activity, and protein in leaves were higher, malondialdehyde(MDA) and hydrogen peroxide(H2O2) decreased, while the activities of superoxide dismutase(SOD), catalase(CAT), and peroxidase(POD) increased. Meanwhile, seedlings were inoculated with two strains of ectomycorrhizal fungi respectively, and the above physiological indices trended the same changes. Moreover, the effect of strain Calvatia lilacina was higher than that of VA mycorrhizal fungi.
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PMID:[Effects of different mycorrhizal fungi on physiological metabolism of tobacco seedlings]. 1196 28

This article reviews the relationship between the energy status of plant cells under O(2) stress (e.g. waterlogging) and the maintenance of membrane intactness, using information largely derived from suspension cultures of anoxia-intolerant potato cells. Energy-related parameters measured were fermentation end-products (ethanol, lactate, alanine), respiratory rate, ATP, adenylate energy charge, nitrate reductase activity and biomass. ATP synthesis rates were calculated from the first four parameters. Reactive oxygen species were estimated from H(2)O(2) and superoxide levels, and the enzymatic detoxification potential from the activity levels of catalase and superoxide dismutase. Structure-related parameters were total fatty acids, free fatty acids (FFAs), lipid hydroperoxides, total phospholipids, N-acylphosphatidylethanolamine (NAPE) and cell viability. The following issues are addressed in this review: (1) what is the impact of anoxia on membrane lipids and how does this relate to energy status; (2) does O(2) per se play a role in these changes; (3) under which conditions and to what extent does lipid peroxidation occur upon re-aeration; and (4) can the effects of re-aeration be distinguished from those of anoxia? The emerging picture is a reappraisal of the relative contributions of anoxia and re-aeration. Two successive phases (pre-lytic and lytic) characterize potato cells under anoxia. They are connected by a threshold in ATP production rate, below which membrane lipids are hydrolysed to FFAs, and NAPE increases. Since lipid peroxidation occurs only when cells are reoxygenated during the lytic phase, its biological relevance in an already damaged system is questionable.
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PMID:Impact of oxygen stress and energy availability on membrane stability of plant cells. 1232 74

Zn efficiency (ZE) is the ability of plants to maintain high yield under Zn-deficiency stress in the soil. Two bean ( Phaseolus vulgaris L.) genotypes that differed in ZE, Voyager (Zn-efficient) and Avanti (Zn-inefficient), were used for this investigation. Plants were grown under controlled-environment conditions in chelate-buffered nutrient solution where Zn(2+) activities were controlled at low (0.1 pM) or sufficient (150 pM) levels. To investigate the relative contribution of the root versus the shoot to ZE, observations of Zn-deficiency symptoms in reciprocal grafts of the two genotypes were made. After growth under low-Zn conditions, plants of nongrafted Avanti, self-grafted Avanti and reciprocal grafts that had the Avanti shoot scion exhibited Zn-deficiency symptoms. However nongrafted and self-grafted Voyager, as well as reciprocal grafts with the Voyager shoot scion, were healthy with no visible Zn-deficiency symptoms under the same growth conditions. More detailed investigations into putative shoot-localized ZE mechanisms involved determinations of leaf biomass production and Zn accumulation, measurements of subcellular Zn compartmentation, activities of two Zn-requiring enzymes, carbonic anhydrase and Cu/Zn-dependent superoxide dismutase (Co/ZnSOD), as well as the non-Zn-requiring enzyme nitrate reductase. There were no differences in shoot tissue Zn concentrations between the Zn-inefficient and Zn-efficient genotypes grown under the low-Zn conditions where differences in ZE were exhibited. Shoot Zn compartmentation was investigated using radiotracer ((65)Zn) efflux analysis and suggested that the Zn-efficient genotype maintains higher cytoplasmic Zn concentrations and less Zn in the leaf-cell vacuole, compared to leaves from the Zn-inefficient genotype under Zn deficiency. Analysis of Zn-requiring enzymes in bean leaves revealed that the Zn-efficient genotype maintains significantly higher levels of carbonic anhydrase and Cu/ZnSOD activity under Zn deficiency. While these data are not sufficient to allow us to determine the specific mechanisms underlying ZE, they certainly point to the shoot as a key site where ZE mechanisms are functioning, and could involve processes associated with Zn compartmentation and biochemical Zn utilization.
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PMID:The role of shoot-localized processes in the mechanism of Zn efficiency in common bean. 1464 15


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