Nitrate reductase ammonium

Hemoprroteins contain heme Hemoglobin Cytochrome e Catalase Nitrate reductase Ammonium oxidase ... 

NH+ Nonactin or dinactin Activity of nitrate reductase, ammonium in mineral water, fruit juice, beer, urine, sewage water 138... 

M. A. Adams and P. M. Attiwill, Nitrate reductase activity and growth response of forest species to ammonium and nitrate sources of nitrogen. Plant Soil 66 373 (1982). 

Oaks, A., Poulle, M., Goodfellow, V.J., Cass, L.A. Deising, H. (1988). The role of nitrate and ammonium ions and light on the induction of nitrate reductase in maize leaves. Plant Physiology 88, 1067-72. 

Padidam, M., Venkatesvarlu, K. Johri, M.M. (1991). Ammonium represses NADPH-nitrate reductase in the moss Funaria hygrometrica. Plant Science 75, 184-94. 

Similar mechanisms operate in the action of nitrate reductase and nitrite reductase. Both of these substances are produced from ammonia by oxidation. Plants and soil bacteria can reduce these compounds to provide ammonia for metabolism. The common agricultural fertilizer ammonium nitrate, NH4NO3, provides reduced nitrogen for plant growth directly, and by providing a substrate for nitrate reduction. NADH or NADPH is the electron donor for nitrate reductase, depending on the organism. 

Berges, J. A., Cochlan, W. P., and Harrison, P. J. (1995). Laboratory and field responses of algal nitrate reductase to diel periodicity irradiance, nitrate exhaustion, and the presence of ammonium. Mar. Ecol. Prog. Ser. 124, 259—269. 

Oxidized forms of nitrogen such as nitrate, need to first be reduced to ammonium before their incorporation into biomass. Nitrate is first reduced by the enzyme assimdatory nitrate reductase to nitrite. Assimilatory nitrite reduction subsequendy reduces the nitrite to ammonium (D Elia and Webb, 1977) (Fig. 21.IE) (see Chapter 7, MuUioUand and Lomas, this volume). 

Young, E. B., Dring, M. J., and Berges, J. A. (2007b). Distinct patterns of nitrate reductase activity in brown algae Light and ammonium sensitivity in Laminaria digitata is absent in Fucus species. J. Phycol. 43, 1200-1208. 

Figure 12 A diagram of the nitrogen cycle with catalyzing enzymes and metal requirements of each step. NIT, nitrogenase AMO, ammonium mono-oxygenase HAO, hydroxylamine oxidoreductase NAR, membrane-bound respiratory nitrate reductase NAP, periplasmic respiratory nitrate reductase NR, assimila-tory nitrate reductase NIR, respiratory nitrite reductase NiR, assimilatory nitrite reductase NOR, nitric oxide reductase N2OR, nitrous oxide reductase.

This two-electron reduction uses NADH or NADPH as electron donor depending on the particular nitrate reductase (EC 1.7.1.1 or EC 1.7.1.2, respectively). Nitrite is then reduced to ammonium in a six-electron process that involves the transfer of three electron pairs from NAD(P)H ... 

Ries and Cast (1965) observed a 90% increase in the nitrogen content of maize leaves with a low level of nitrogen-supply after two simazine treatments of 10 mole/dm. Similar results have been reported by Tweedy and Ries (1967) for maize grown at suboptimal temperature and low nitrogen supply. On the other hand, simazine did not enhance the growth of maize plants if the nitrogen was supplied in the form of ammonium. In maize plants treated with simazine, the nitrate reductase activity is increased by one order of magnitude under suboptimal conditions. 

Molecular mechanisms of nitrate accumulation depend not only on the nitrate reductase system, but also on the ability of roots to take from the soil, nitrate or ammonium ions, and on the plant s capacity for their conversion by assimilation processes to higher products. Besides this, the assimilation depends on the ability of a given genotype to transport substances necessary for the synthesis. It was shown that genotype differences of the nitrate reductase level do not depend on the nitrate content in tissues [25]. Nitrates are accumulated in plant organisms at high concentrations when aU the nitrogen accepted cannot be utilized for the production of amino acids and for subsequent protein synthesis [26]. This occurs when the plant, in the course of its metabolism, is unable to reduce the accepted nitrates into the assimilable ammonia form. 

Nitrate reductase is an inducible enzyme and is usually found only in the presence of nitrate. Nitrate reductase is the logical point to effect regulation of the input of reduced nitrogen for the plant because it is the first and normally the rate limiting enzyme between nitrate and amino-N. The toxic effects of excess levels of nitrite and ammonium ions also indicate the desirability of regulating their production. 

An apparent requirement for RNA synthesis, specifically D-RNA (Ingle, 1968), implies that nitrate may be acting as a co-inducer of nitrate reductase synthesis in the classical sense of the model proposed by Jacob and Monod (1%1). Choudary and Rao (1976) have suggest on the basis of inhibitor studies with Candida utilis that nitrate functions at the transcriptional level. However, Hipkin and Syrett (1977) reported that several algae grown on ammonium and lacking nitrate reductase activity, contained preformed messenger-RNA for nitrate reductase synthesis and concluded that nitrate operates at the post-transcriptional level. 

The mechanism of repression of induction of nitrate reductase by ammonium in fungal systems is not understood. It has been suggested (Dantzig et al., 1978 Premakumar et al., 1978 Subramanian et al., 1%8) that glutamine or... 

The cessation of nitrate reduction on transfer of green algae to ammonium has been attributed to the uncoupling effect of this ion on noncyclic photo-phosphorylatim and a resultant increase in intracellular reducing power and ADP. Supporting this proposal are the findings that arsenate can duplicate the ammonium effect and the inactivation by anunonium ions can be prevented by treatment of cells with DCMU, an inhibitor of photosynthetic electron transfer (Losada, 1973, 1975 Chaparro et al., 1976). It has been demonstrated that ADP and/or NADH inactivate nitrate reductase in vitro... 

Pistorius et al. (1978) have indicated that the time course kinetics of accumulation of cyanide inactivated enzyme observed, when cells of Chlorella are transferred from nitrate to ammonium, are too slow to account for the measured rapid decline in nitrate reduction. They suggest that cessation of nitrate utilization when this organism is transferred to ammonium is due to a termination of nitrate uptake. However, Diez et al. (1977) indicated that in Ankistrodesmus the absence of a nitrogen source (i.e., no nitrate uptake) brings about a much smaller inactivation of nitrate reductase than that produced by the transfer from nitrate to ammonium. Thus, the rapid in vivo inactivation of nitrate reduction observed in this alga when it is transferred to... 

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