Nitrosating activity in Escherichia coli

Nitrosation activity was measured in Escherichia coli isolates and a range of nitrite reductase (nir) mutants. Activity was only detected in intact cells and could be inhibited by a number of treatments such as sonication and osmotic shock. Aerobically-grown cells had highest nitrosation activity compared to oxygen-limited ones. Inclusion of nitrite in growth media induced high activities of nitrite reductase and for some isolates, nitrosation. Analysis of nir mutants identified two which were unable to nitrosate. This result suggested that NADH-dependent nitrite reductase was implicated either directly or indirectly in nitrosation.     

Nonthermal effect of microwave irradiation on nitrite uptake in Chlamydomonas reinhardtii

When cells of the unicellular green alga Chlamydomonas reinhardtii were subjected to microwave irradiation at 2.45 GHz, nitrite uptake kinetics still obeyed the Michaelis-Menten equation, the Km of the process remaining constant, whereas V _max increased, which indicates an enhanced nonthermal permeability in irradiated cells.     

Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4

Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h^–1) nitrate and nitrite reductase activities of 200 nmol · mg^–1 protein · min^–1 and 250 nmol · mg^–1 protein · min^–1 were measured, respectively. At a high growth rate (0.55 h^–1) both enzyme activities were considerably lower (25 and 12 nmol mg^–1 · protein · min^–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.     

Nitrite reduction in Bacteroids of Rhizobium “hedysari” strain HCNT 1

Ex planta, bacteroids of the sulla-symbiont Rhizobium hedysari strain HCNT 1 terminated reduction of nitrite at nitrous oxide irrespective of the presence or absence of acetylene. Nitrate was not reduced during the experimental period, but slight nitrate reductase activity occurred if incubation with nitrate was prolonged (up to 15 h). As was observed in free-living cells, exposure of the bacteroids to the metal chelator, diethyldithiocarbamate, prevented reduction of nitrite, indicating the presence of a copper-containing nitrite reductase. Pulses of 10–75 M nitrite transiently impeded O₂ uptake in bacteroids, which resumed consumption of O₂ when the nitrite had been reduced. Exposure to >1.0 mM nitrite for 24h greatly inhibited nitrogenase activity (assayed as acetylene reduction activity) of bacteroids in planta. Exposure to the same concentrations of nitrite after 1h of incubation in the presence of acetylene almost completely stopped ongoing ethylene production in bacteroids of strain HCNT 1 extracted from nodules. Free cells of the non-nitrite-reducing R. hedysari strain CC 1335 were lacking in nitrogenase (acetylene-reduction) activity, whereas identically cultured (low-oxygen) strain HCNT 1 cells reduced both nitrite and acetylene.Abbreviations PMS phenazine methosulfate - DDC diethyldithiocarbamate     

The influence of oxygen concentrations on denitrification in soil

Summary The influence of different O₂ concentrations on denitrification was studied in an agricultural soil. In both nitrate and nitrite amended soil, denitrification was not observed until the O₂ concentration decreased to 0.20 and 0.21 mol/ml, respectively. Denitrification was not observed in soil samples with O₂ concentrations above 0.28 mol/ml in the gas phase. These findings suggest that a completely anoxic environment is not required for denitrification to occur in soil.     

Nitrate reductase is not accumulated in chloroplast-ribosome-deficient mutants of higher plants

The activities of nitrite reductase (EC 1.7.7.1) are 60–70% of wild-type activity in pigment-deficient leaves of the chloroplast-ribosomedeficient mutants albostrians (Hordeum vulgare) and iojap (Zea mays). The activity and apoprotein of nitrate reductase (EC 1.6.6.1.) are lacking in the barley mutant. Only very low activities of nitrate reductase can be extracted from leaves of the maize mutant. The molybdenum cofactor of nitrate reductase and xanthine dehydrogenase (EC 1.2.3.2) is present in maize and barley mutant plants. However, it is not inducible by nitrate in pigment-deficient leaves of albostrians. From these results we conclude: (i) Nitrite reductase (a chloroplast enzyme) is synthesized in the cytoplasm and does not need the presence of nitrate reductase for the induction and maintenance if its activity. (ii) The loss or low activity of nitrate reductase is a consequence of the inability of the mutants to accumulate the apoprotein of this enzyme. (iii) The chloroplasts influence the accumulation (i.e. most probably the synthesis) of the nonchloroplast enzyme, nitrate reductase. The accumulation of nitrate reductase needs a chloroplast factor which is not provided by mutant plastids blocked at an early stage of their development.Abbreviations CRM cross-reacting material - Mo-co molybdenum cofactor - NiR nitrite reductase - NR nitrate reductase     

Analysis of the energy metabolism after incubation of Saccharomyces cerevisiae with sulfite or nitrite

After addition of 5 mM sulfite or nitrite to glucose-metabolizing cells of Saccharomyces cerevisiae a rapid decrease of the ATP content and an inversely proportional increase in the level of inorganic phosphate was observed. The concentration of ADP shows only small and transient changes. Cells of the yeast mutant pet 936, lacking mitochondrial F₁ATPase, after addition of 5 mM sulfite or nitrite exhibit changes in ATP, ADP and inorganic phosphate very similar to those observed in wild type cells. They key enzyme of glucose degradation, glyceraldehyde-3-phosphate dehydrogenase was previously shown to be the most sulfiteor nitrite-sensitive enzyme of the glycolytic pathway. This enzyme shows the same sensitivity to sulfite or nitrite in cells of the mutant pet 936 as in wild type cells. It is concluded that the effects of sulfite or nitrite on ATP, ADP and inorganic phosphate are the result of inhibition of glyceraldehyde-3-phosphate dehydrogenase and not of inhibition of phosphorylation processes in the mitochondria. Levels of GTP, UTP and CTP show parallel changes to ATP. This is explained by the presence of very active nucleoside monophosphate kinases which cause a rapid exchange between the nucleoside phosphates. The effects of the sudden inhibition of glucose degradation by sulfite or nitrite on levels of ATP, ADP and inorganic phosphate are discussed in terms of the theory of Lynen (1942) on compensating phosphorylation and dephosphorylation in steady state glucose metabolizing yeast.Abbreviations ATP adenosine triphosphate - ADP adenosine diphosphate - AMP adenosine monophosphate - P_i inorganic orthophosphate Dedicated to Prof. Dr. Hans Grisebach on the occasion of his sixtieth birthday     

Nitrous oxide production by cyanobacteria

Evidence is presented here that axenic cultures of Nostoc spp., Aphanocapsa (PCC 6308), and Aphanocapsa (PCC 6714) but not Anacystis nidulans R-2 (PCC 7942) produce N₂O and ammonia when grown on nitrite. The data suggest that the cyanobacteria produce N₂O by nitrite reduction to ammonia.Nonstandard abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - NIR nitrite reductase