Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chloroplasts were prepared from peas (Pisum sativum) in glucose-phosphate medium. In the presence of dl-glyceraldehyde, they catalyzed nitrite-dependent O(2) evolution (mean of 13 preparations, 17.5 mumole per mg chlorophyll per hour, sd 3.64). The optimum concentration of nitrite was 0.5 mm; 0.12 mm nitrite supported V(max)/2. The reaction was accompanied by the consumption of nitrite; 55 to 80% of the nitrite-N consumed was recovered as ammonia. In short experiments (less than 10 minutes) the O(2) to nitrite ratio approached 1.5, but thereafter decreased. There was no nitrite-dependent O(2) evolution with chloroplasts from plants grown without added nitrate but such chloroplasts could assimilate ammonia at about the usual rate. The results are consistent with the reduction of nitrite to ammonia involving nitrate-induced nitrite reductase and a reductant generated by the chloroplast electron transport chain.In the presence of ADP, pyrophosphate, and MgCl(2) the O(2) to nitrite ratio was typically 0.5 to 0.6 and the recovery of nitrite-N as ammonia about 60%. Under these conditions, alpha-ketoglutarate increased the O(2) to nitrite ratio (0.9-1.35) and the recovery of nitrite-N as ammonia decreased to 27%. These data and the results of nitrite plus ammonia addition experiments (with and without alpha-ketoglutarate) are attributed to incorporation of nitrite-N into glutamate via the chloroplast enzymes nitrite reductase, glutamine synthetase, and glutamate synthetase.
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PMID:Light-dependent Assimilation of Nitrite by Isolated Pea Chloroplasts. 1666 Mar 65

Nitric oxide (NO) is a signaling and defense molecule of major importance in living organisms. In the model legume Medicago truncatula, NO production has been detected in the nitrogen fixation zone of the nodule, but the systems responsible for its synthesis are yet unknown and its role in symbiosis is far from being elucidated. In this work, using pharmacological and genetic approaches, we explored the enzymatic source of NO production in M. truncatula-Sinorhizobium meliloti nodules under normoxic and hypoxic conditions. When transferred from normoxia to hypoxia, nodule NO production was rapidly increased, indicating that NO production capacity is present in functioning nodules and may be promptly up-regulated in response to decreased oxygen availability. Contrary to roots and leaves, nodule NO production was stimulated by nitrate and nitrite and inhibited by tungstate, a nitrate reductase inhibitor. Nodules obtained with either plant nitrate reductase RNA interference double knockdown (MtNR1/2) or bacterial nitrate reductase-deficient (napA) and nitrite reductase-deficient (nirK) mutants, or both, exhibited reduced nitrate or nitrite reductase activities and NO production levels. Moreover, NO production in nodules was found to be inhibited by electron transfer chain inhibitors, and nodule energy state (ATP-ADP ratio) was significantly reduced when nodules were incubated in the presence of tungstate. Our data indicate that both plant and bacterial nitrate reductase and electron transfer chains are involved in NO synthesis. We propose the existence of a nitrate-NO respiration process in nodules that could play a role in the maintenance of the energy status required for nitrogen fixation under oxygen-limiting conditions.
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PMID:Both plant and bacterial nitrate reductases contribute to nitric oxide production in Medicago truncatula nitrogen-fixing nodules. 2113 86

Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain (ETC) that has a lower affinity for oxygen than does cytochrome (cyt) oxidase. To investigate the role(s) of AOX under different oxygen conditions, wild-type (WT) Nicotiana tabacum plants were compared with AOX knockdown and overexpression plants under normoxia, hypoxia (near-anoxia), and during a reoxygenation period following hypoxia. Paradoxically, under all the conditions tested, the AOX amount across plant lines correlated positively with leaf energy status (ATP/ADP ratio). Under normoxia, AOX was important to maintain respiratory carbon flow, to prevent the mitochondrial generation of superoxide and nitric oxide (NO), to control lipid peroxidation and protein S-nitrosylation, and possibly to reduce the inhibition of cyt oxidase by NO. Under hypoxia, AOX was again important in preventing superoxide generation and lipid peroxidation, but now contributed positively to NO amount. This may indicate an ability of AOX to generate NO under hypoxia, similar to the nitrite reductase activity of cyt oxidase under hypoxia. Alternatively, it may indicate that AOX activity simply reduces the amount of superoxide scavenging of NO, by reducing the availability of superoxide. The amount of inactivation of mitochondrial aconitase during hypoxia was also dependent upon AOX amount, perhaps through its effects on NO amount, and this influenced carbon flow under hypoxia. Finally, AOX was particularly important in preventing nitro-oxidative stress during the reoxygenation period, thereby contributing positively to the recovery of energy status following hypoxia. Overall, the results suggest that AOX plays a beneficial role in low oxygen metabolism, despite its lower affinity for oxygen than cytochrome oxidase.
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PMID:Roles for Plant Mitochondrial Alternative Oxidase Under Normoxia, Hypoxia, and Reoxygenation Conditions. 3249 3