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)

The in situ localization of the chloroplast enzymes ribulose-1,5-bisphosphate carboxylase (Rubisco), Rubisco activase, ribose-5-phosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, aldolase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase was studied by immunoelectron microscopy in Chlamydomonas reinhardtii. Immunogold labeling revealed that, despite Rubisco in the pyrenoid matrix, Calvin cycle enzymes, Rubisco activase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase are associated predominantly with chloroplast thylakoid membranes and the inner surface of the pyrenoid membrane. This is in accord with previous enzyme localization studies in higher plants (K.H. Suss, C. Arkona, R. Manteuffel, K. Adler [1993] Proc Natl Acad Sci USA 90: 5514-5518). Pyrenoid tubules do not contain these enzymes. The pyrenoid matrix consists of Rubisco but is devoid of the other photosynthetic enzymes investigated. Evidence for the occurrence of two Rubisco forms differing in their spatial localization has also been obtained: Rubisco form I appears to be membrane associated like other Calvin cycle components, whereas Rubisco form II is confined to the pyrenoid matrix. It is proposed that enzyme form I represents an active Rubisco when assembled into Calvin cycle enzyme complexes, whereas Rubisco form II may be part of a CO2-concentrating mechanism. Pyrenoidal Calvin cycle complexes are thought to be highly active in CO2 fixation and important for the synthesis of starch around the pyrenoid.
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PMID:In Situ Association of Calvin Cycle Enzymes, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase, Ferredoxin-NADP+ Reductase, and Nitrite Reductase with Thylakoid and Pyrenoid Membranes of Chlamydomonas reinhardtii Chloroplasts as Revealed by Immunoelectron Microscopy. 1222 43

The localization of enzymes responsible for nitrate assimilation and the generation of NADH for nitrate reduction were studied in corn (Zea mays L.) leaf blades. The techniques used effectively separated mesophyll and bundle sheath cells as judged by microscopic observations, enzymic assays, chlorophyll a/b ratios and photochemical activities. Nitrate reductase, nitrite reductase, and the nitrate content of leaf blades were localized primarily in the mesophyll cells, although some nitrite reductase was found in the bundle sheath cells. Glutamine synthetase, NAD-malate dehydrogenase, NAD-glyceraldehyde-3-phosphate dehydrogenase, and NADP-glutamate dehydrogenase were found in both types of cells, however, more NADP-glutamate dehydrogenase was found in the bundle sheath cells than in the mesophyll cells. These data indicate that the mesophyll cells are the major site for nitrate assimilation in the leaf blade because they contained an ample supply of nitrate and the enzymes considered essential for the assimilation of nitrate into amino acids. Because the specific activity of nitrate reductase was severalfold lower than the other enzymes involved in nitrate assimilation, nitrate reduction is indicated as the rate-limiting step in situ. A sequence of reactions is proposed for nitrate assimilation in the mesophyll cells of corn leaves as related to the C-4 pathway of photosynthesis.
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PMID:Pathway for Nitrate Assimilation in Corn (Zea mays L.) Leaves: Cellular Distribution of Enzymes and Energy Sources for Nitrate Reduction. 1666 May 71

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