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)

Sucrose catabolism was studied in Rhodopseudomonas capsulata. Sucrose was hydrolysed by the action of a constitutive cytoplasmic sucrase. The use of a glucose-6-phosphate dehydrogenase-deficient mutant and radiorespirometric experiments demonstrated that both the glucose and fructose moieties of sucrose were catabolized via the Entner-Doudoroff pathway. This result was confirmed by enzyme analysis and studies on sugar assimilation. All the enzymes of the Entner-Doudoroff pathway were present in bacteria grown on secrose but fructokinase (EC 1.7.1.4) activity was relatively low. In contrast, phosphoenolpyruvate:fructose phosphotransferase and 1-phosphofructokinase, the key enzymes for the catabolism of exogenous fructose, were only partially induced. Bacteria grown on sucrose and treated with chloramphenicol were, therefore, not able to assimilate exogenous fructose. We conclude that under these conditions endogenous fructose is catabolized via the Entner-Douboroff pathway, while exogenous fructose is degraded via fructose 1-phosphate and the Embden-Meyerhof pathway.
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PMID:An alternative pathway for the degradation of endogenous fructose during the catabolism of sucrose in Rhodopseudomonas capsulata. 64 27

An NADPH-dependent NO2--reducing system was reconstituted in vitro using ferredoxin (Fd) NADP+ oxidoreductase (FNR), Fd, and nitrite reductase (NiR) from the green alga Chlamydomonas reinhardtii. NO2- reduction was dependent on all protein components and was operated under either aerobic or anaerobic conditions. NO2- reduction by this in vitro pathway was inhibited up to 63% by 1 mm NADP+. NADP+ did not affect either methyl viologen-NiR or Fd-NiR activity, indicating that inhibition was mediated through FNR. When NADPH was replaced with a glucose-6-phosphate dehydrogenase (G6PDH)-dependent NADPH-generating system, rates of NO2- reduction reached approximately 10 times that of the NADPH-dependent system. G6PDH could be replaced by either 6-phosphogluconate dehydrogenase or isocitrate dehydrogenase, indicating that G6PDH functioned to: (a) regenerate NADPH to support NO2- reduction and (b) consume NADP+, releasing FNR from NADP+ inhibition. These results demonstrate the ability of FNR to facilitate the transfer of reducing power from NADPH to Fd in the direction opposite to that which occurs in photosynthesis. The rate of G6PDH-dependent NO2- reduction observed in vitro is capable of accounting for the observed rates of dark NO3- assimilation by C. reinhardtii.
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PMID:In vitro reconstitution of electron transport from glucose-6-phosphate and NADPH to nitrite 957

Physiological alterations and regulation of heterocyst and nitrogenase formation have been studied in Het(-) Fix(-) mutant strain of diazotrophic cyanobacterium Anabaena variabilis. Het(-) Fix(-) mutant strain of A. variabilis has been isolated by N-methyl-N'-nitro-N"-nitrosoguanidine (NTG) mutagenesis and was screened with the penicillin enrichment (500 microg ml(-1)). Growth, heterocyst differentiation, nitrogenase and glutamine synthetase (biosynthetic and transferase), (14)CO(2)-fixation, nitrate reductase (NR), nitrite reductase (NiR), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (IDH) activities, and NO(3)(-), NO(2)(-), and NH(4)(+) uptake and whole cell protein profile in different metabolic conditions were studied in the Het(-) Fix(-) mutant strain taking wild-type A. variabilis as reference. Het(-) Fix(-) mutant strain was incapable of assimilating elemental nitrogen (N(2)) due to its inability to form heterocysts and nitrogenase and this was the reason for its inability to grow in BG-11(0) medium (free from combined nitrogen). In contrast, wild-type strain grew reasonably well in the absence of combined nitrogen sources and also showed heterocyst differentiation (8.5%) and nitrogenase activity (10.8 etamol C(2)H(4) formed microg(-1) Chl a h(-1)) in N(2)-medium. Wild-type strain also exhibited higher NR, NiR, and GS activities compared to its Het(-) Fix(-) mutant strain, which may presumably be due to acquisition of high uptake of NO(3)(-), NO(2)(-), and NH(2)(+). Wild-type strain in contrast to its Het(-) Fix(-) mutant strain also exhibited high level of G6PDH, IDH, and (14)CO(2) fixation activities. Low levels of G6PDH and IDH activities in Het(-) Fix(-) mutant strain further confirmed the lack of heterocyst differentiation and nitrogenase activity in the Het(-) Fix(-) mutant strain.NR, NiR, and GS activities in both the strains were energy-dependent and the energy required is mainly derived from photophosphorylation. Furthermore, it was found that de novo protein synthesis is necessarily required for the activities of NR, NiR, and GS in both wild-type and its Het(-) Fix(-) mutant strain.
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PMID:Physiological alterations and regulation of heterocyst and nitrogenase formation in Het(-) Fix(-) mutant strain of Anabaena variabilis. 1223 60

In roots, nitrate assimilation is dependent upon a supply of reductant that is initially generated by oxidative metabolism including the pentose phosphate pathway (OPPP). The uptake of nitrite into the plastids and its subsequent reduction by nitrite reductase (NiR) and glutamate synthase (GOGAT) are potentially important control points that may affect nitrate assimilation. To support the operation of the OPPP there is a need for glucose 6-phosphate (Glc6P) to be imported into the plastids by the glucose phosphate translocator (GPT). Competitive inhibitors of Glc6P uptake had little impact on the rate of Glc6P-dependent nitrite reduction. Nitrite uptake into plastids, using (13)N labelled nitrite, was shown to be by passive diffusion. Flux through the OPPP during nitrite reduction and glutamate synthesis in purified plastids was followed by monitoring the release of (14)CO(2) from [1-(14)C]-Glc6P. The results suggest that the flux through the OPPP is maximal when NiR operates at maximal capacity and could not respond further to the increased demand for reductant caused by the concurrent operation of NiR and GOGAT. Simultaneous nitrite reduction and glutamate synthesis resulted in decreased rates of both enzymatic reactions. The enzyme activity of glucose 6-phosphate dehydrogenase (G6PDH), the enzyme supporting the first step of the OPPP, was induced by external nitrate supply. The maximum catalytic activity of G6PDH was determined to be more than sufficient to support the reductant requirements of both NiR and GOGAT. These data are discussed in terms of competition between NiR and GOGAT for the provision of reductant generated by the OPPP.
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PMID:The effect of Glc6P uptake and its subsequent oxidation within pea root plastids on nitrite reduction and glutamate synthesis. 1722 May 12

Plastids from roots of barley (Hordeum vulgare L.) seedlings were isolated by discontinuous Percoll-gradient centrifugation. Coinciding with the peak of nitrite reductase (NiR; EC 1.7.7.1, a marker enzyme for plastids) in the gradients was a peak of a glucose-6-phosphate (Glc6P) and NADP(+)-linked nitrite-reductase system. High activities of phosphohexose isomerase (EC 5.3.1.9) and phosphoglucomutase (EC 2.7.5.1) as well as glucose-6-phosphate dehydrogenase (Glc6PDH; EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) were also present in the isolated plastids. Thus, the plastids contained an overall electron-transport system from NADPH coupled with Glc6PDH and 6PGDH to nitrite, from which ammonium is formed stoichiometrically. However, NADPH alone did not serve as an electron donor for nitrite reduction, although NADPH with Glc6P added was effective. Benzyl and methyl viologens were enzymatically reduced by plastid extract in the presence of Glc6P+ NADP(+). When the plastids were incubated with dithionite, nitrite reduction took place, and ammonium was formed stoichiometrically. The results indicate that both an electron carrier and a diaphorase having ferredoxin-NADP(+) reductase activity are involved in the electron-transport system of root plastids from NADPH, coupled with Glc6PDH and 6PGDH, to nitrite.
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PMID:Nitrite reduction in barley-root plastids: Dependence on NADPH coupled with glucose-6-phosphate and 6-phosphogluconate dehydrogenases, and possible involvement of an electron carrier and a diaphorase. 2424 Sep 61

The effect of nitrate incubation on the pattern of carbohydrate metabolism in different regions of the pea (Pisum sativum L. var. Kelvedon Wonder) root has been studied. Roots were incubated in a 10 mM potassium nitrate solution for 4, 8 and 12 h. Marked increases were noted in the activities of nitrate assimilation enzymes after 4 h. Increased activities were also recorded for hexokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and transketolase. No consistent changes were observed in the activities of phosphofructokinase and glyceraldehyde-3-phosphate dehydrogenase. Experiments with [1-(14)C] and [6-(14)C]glucose indicated a relative shift in the pattern of carbohydrate oxidation from glycolysis to the pentose phosphate pathway. The data are interpreted as indicating a close interrelationship between nitrate assimilation and carbohydrate metabolism, particularly in relation to the supply of NADPH by the pentose phosphate pathway for nitrite reductase.
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PMID:Interrelationship between nitrate assimilation and carbohydrate metabolism in plant roots. 2444 67

Enzymes representative of, and related to, the pentose phosphate pathway, glycolysis, and the tricarboxylic acid cycle have been demonstrated in supernatant and lamellar fractions of Anabaena cylindrica cultured in the presence of atmospheric nitrogen, ammonia, nitrite, and nitrate. Nitrogen-fixing and ammonia-assimilating algae contained essentially similar levels of most enzymes tested, with the notable exception of glyceraldehyde-3-phosphate dehydrogenase which showed increased NADPH-linked activity with concomitant diminution of NADH-linked activity when ammonia was supplied. The provision of nitrite or nitrate caused significant enhancements of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and the related hexokinase and phosphohexoisomerase. Reduced activities of pyruvate kinase, malate dehydrogenase, phosphoenolpyruvate carboxylase, and both NADH and NADPH oxidoreductases were recorded for nitrate-grown alga.The stimulation of the pentose phosphate pathway, at the partial expense of glycolysis and the tricarboxylic acid cycle, in algae cultured with nitrite and nitrate was interpreted to be due to additional NADPH requirements imposed by induced nitrite reductase. Modification of the pyridine nucleotide linkage of glyceraldehyde-3-phosphate dehydrogenase and the oxidoreductases was attributed to diversion of reductant to nitrite and nitrate reductases and nitrogenase. The results are considered to indicate regulation of blue-green algal metabolism determined by the availability of pyridine nucleotides.
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PMID:The influence of inorganic nitrogen supply on carbohydrate and related metabolism in the blue-green alga, Anabaena cylindrica Lemm. 2445 90