Assimilatory

Assimilatory nitrate reduction Conversion of nitrate to reduced forms of nitrogen, generally ammonium, for the synthesis of amino acids and proteins. 

Assimilatory denitrifiers reduce nitrate to the amino acid level where it is incorporated into protein. Many plants and bacteria can do this and, therefore, use nitrate as a nitrogen source. 

Assimilatory nitrate reduction is the reduction of NOT, followed by uptake of the nitrogen by the organism as biomass. 

In order to check whether the occurrence of the Rieske-type sequence motif is unique for the assimilatory nitrite reductase from Bacillus subtilis, the sequences of other assimilatory nitrite reductases were searched for the presence of the four putative ligands of Rieske-type clusters. A well-conserved sequence pattern... 

There are four different classes of nitrate reductases (234). The nitrate reductases from D. desulfuricans show a strong homology to the a-subunit of the class of periplasmic respiratory nitrate reductases, and also to some of the enzymes that are included on the class of cytoplasmic assimilatory nitrate reductases. Because of this fact, a proposal was made for a new class of monomeric NAP, which contains the minimal arrangement of metal centers to perform nitrate reduction one [4Fe-4S] cluster and a Mo bound to two MGD. 

The energy and reducing power necessary (E) for the synthesis of cell substance, i. e., growth and multiplication, can be made available simultaneously with the synthesis of the central precursor. If this assimilatory energy (Ea) is not sufficient (Ea< E) to convert the precursor-carbon completely into biomass, further substrate must be dissimilated. 

Figure 3. The general nitrogen model for illustrating the bio geochemical cycling in Forest ecosystems. Explanations for the fluxes 1, ammonia volatilization 2, forest fertilization 3, N2-fixation 4, denitrification 5, nitrate respiration 6, nitrification 7, immobilization 8, mineralization 9, assimilatory and dissimilatory nitrate reduction to ammonium 10, leaching 11, plant uptake 12, deposition N input 13, residue composition, exudation 14, soil erosion 15, ammonium fixation and release by clay minerals 16, biomass combustion 17, forest harvesting 18, litterfall (Bashkin, 2002).

Assimilatory Fe metabolism Fe biomolecules (siderophores, ferritin) magnetite (magnetotactic bacteria). 

Figure 17.1. Phylogenetic tree based on 16S rDNA sequence analysis showing the placement of the novel chemolithoautotrophic Fe(III) reducers. Capital and bold face letters, respiratory Fe(III) reducers , tested heterotrophic species that probably reduce Fe(III) predominantly in an assimilatory fashion.

In the second step, 32 mol O2 are generated from the assimilatory reduction of nitrate, in the form of HNO3, amine nitrogen, represented in the organic molecule as (NHj) , ... 

Nitrogen uptake that results in the formation of new biomolecules is termed an assimilation process, such as assimilatory nitrogen reduction. The processes that result in the release of DIN into seawater are referred to as dissimilations, such as dissimi-latory nitrogen reduction. An example of the latter is denitrification, in which nitrate and nitrite obtained from seawater serve as electron acceptors to enable the oxidation of organic matter. This causes the nitrate and nitrite to be transformed into reduced species, such as N2O and N2, which are released back into seawater. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

This process is commonly referred to as assimilatory nitrogen (nitrate or nitrite) reduction. The electrons for these reductions are supplied by half-cell oxidations involving NADPH/NADP" and NADH/NAD" (Table 7.11). All of these reactions and membrane transport processes are mediated by enzymes that are specific to the DIN species. Considerable variation exists among the phytoplankton species in their ability to produce the necessary enzymes. Since marine phytoplankton are often nitrogen limited, the quantity and type of DIN available in the water column can greatly influence overall phytoplankton abundance and species diversity. 

Like assimilatory nitrogen reduction, denitrification proceeds through a series of steps with nitrate first being reduced to nitrite, followed by reduction of nitrite to N2(g). Under some conditions, N20(g) is also produced. 

Assimilatory nitrate reduetion The reduction of nitrate to organic nitrogen compounds that constitute the tissues of marine organisms. Plankton and some bacteria assimilate nitrogen via this process. 

Assimilatory NOs reduction might also occur. But because concentrations of NH4+ and organic N are in general large in anaerobic environments, it is suppressed and insignificant. The literature on NOs reduction is reviewed by Tiedje (1988). 

The bis-hydroxylamine adduct [Fe (tpp)(NH20H)2] is stable at low temperatures, but decomposes to [Fe(tpp)(NO)] at room temperature. [Fe(porphyrin)(NO)] complexes can undergo one-and two-electron reduction the nature of the one-electron reduction product has been established by visible and resonance Raman spectroscopy. Reduction of [Fe(porphyrin)(NO)] complexes in the presence of phenols provides model systems for nitrite reductase conversion of coordinated nitrosyl to ammonia (assimilatory nitrite reduction), while further relevant information is available from the chemistry of [Fe (porphyrin)(N03)]. Iron porphyrin complexes with up to eight nitro substituents have been prepared and shown to catalyze oxidation of hydrocarbons by hydrogen peroxide and the hydroxylation of alkoxybenzenes. ... 

Nitrate reductase (NADH) [EC 1.6.6.1], also known as assimilatory nitrate reduetase, eatalyzes the reaction of NADH with nitrate to produee NAD+, nitrite, and water. This enzyme uses FAD or FMN, heme, and a molybdenum ion as eofaetors. (2) Nitrate reductase (NAD(P)H) [EC 1.6.6.2], also known as assimilatory nitrate reduetase, eatalyzes the reaetion of NAD(P)H with nitrate to produee NAD(P)+, nitrite, and water. This enzyme uses FAD or FMN, heme, and a molybdenum ion as eofaetors. (3) Nitrate reductase (NADPH) [EC 1.6.6.3] eatalyzes the reaetion of NADPH with nitrate to produee NADP+, nitrite, and water. This enzyme uses FAD, heme, and a molybdenum ion as cofactors. (4) Nitrate reduetase (eytoehrome) [EC 1.9.6.1] catalyzes the reaetion of nitrate with ferroeytochrome to produce nitrite and ferrieytoehrome. (5) Nitrate reductase (ac-eeptor) [EC 1.7.99.4], also known as respiratory nitrate... 

Assembly-induced GTP hydrolysis, MICROTUBULE ASSEMBLY KINETICS Assimilatory nitrate reductase,... 

With M. gryphiswaldense, Schuler and Bauerlein (1996) recorded an Fe uptake rate from Fe " citrate of 0.86 nmol min mg dry weight and suggested that the major portion of Fe is taken up in an energy-dependent process possibly by a reductive step (Schuler, 1999). Fukumori et al. (1997) proposed that the dissimilatory nitrite reductase of M. magnetotacticum may function as an Fe" oxidizing enzyme. Later, Fuko-mori (2000) suggested an Fe "quinate complex as the source of Fe which is subsequently reduced in the cell in a microaerobic environment at about neutral pH by the iron reductase NADH (an assimilatory enzyme). 

The fact that the cytochrome P-450 was induced even in the presence of NH3, which is the end product of assimilatory N-oxide reductions, suggested that it might funciton in dissimilatory N-oxide reductions. Anaerobic growth experiments with induced cells showed that reduction of nitrate to nitrite was energy yielding in F. oxysporum but reduction of nitrite to N2O was probably not (Shoun and Tanimoto, 1991). 

Vega, J. M., Garrett, R. H., and Siegel, L. M. (1975). Siroheme A prosthetic group of the Neurospora crassa assimilatory nitrite reductases. ]. Biol. Chem. 250, 7980-7989. 

I Without pyrenoids assimilatory products oils.Class Chloromonadineae.Order Trentoniales... 

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