Assimilatory reduction

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) , ... 

Removal of sulfate from the water column can occur by either assimi-latory or dissimilatory reduction. Assimilatory reduction occurs in the water column, whereas uptake by plankton results in the formation of organic S. 

Assimilatory reduction to NH + (ANRA) involves the simultaneous reduction of NO3 - and uptake of N by the organism into biomass, as shown below ... 

Bottcher, M.E., Sievert, S.M., and Kuever, J. (1999) Fractionation of sulfur isotopes during assimilatory reduction of sulfate thermophilic gram-negative bacterium at 60 degrees C. Arch. Microbiol. 172, 125-128. 

Indirect evidence further supporting the phytoplankton partial assimilatory reduction model was presented by Herbland and Voituriez (1979). They performed a statistical analysis of 123 measurements of the depths of the PNM and the top of the nitracline, and found a strong correlation. They also found a significant offset of... 

The biochemical pathway of both assimilatory and dissimilatory sulfate reduction is illustrated in Figure 1. The details of the dissimilatory reduction pathway are useful for understanding the origin of bacterial stable isotopic fractionations. The overall pathways require the transfer of eight electrons, and proceed through a number of intermediate steps. The reduction of sulfate requires activation by ATP (adenosine triphosphate) to form adenosine phosphosulfate (APS). The enzyme ATP sulfurylase catalyzes this reaction. In dissimilatory reduction, the sulfate moiety of APS is reduced to sulfite (SO3 ) by the enzyme APS reductase, whereas in assimilatory reduction APS is further phosphorylated to phospho-adenosine phosphosulfate (PAPS) before reduction to the oxidation state of sulfite and sulfide. Although the reduction reactions occur in the cell s cytoplasm (i.e., the sulfate enters the cell), the electron transport chain for dissimilatory sulfate reduction occurs in proteins that are peiiplasmic (within the bacterial cell wall). The enzyme hydrogenase... 

Acidithiobacillus ferrooxidans 167, 177 Acidoid sol 161, 163 Agriculture 184-185 Allochromatium vinosum 172, 174-176 Allotropes 1, 3-4, 12, 17, 19, 47, 54-57 -, high-pressure 59 Aqueous sulfur sol 154 Assimilatory reduction 169 Aten s sulfur 17... 

ATP sulfurylase, catalyzes the primary step of intracellular sulfate activation, essential for assimilatory reduction of sulfate to sulfide, involved in methionine metabolism... 

Soils inclnding wetland soils are important sonrces of atmospheric nitrous oxide. A wide range of processes may produce nitrous oxide, as well as minor amounts of NO, but not all of these seem to be fully understood. The main biological processes of nitrous oxide formation in soils are shown in Figure 16.5. They include nitrification, denitrification, the dissimilatory reduction of nitrate to ammonium, and the assimilatory reduction of nitrate wherein N is incorporated in the cell biomass. Additionally, some NO and nitrous oxide may be released due to chemo-denitrification and pyro-denitrification. Of these processes, nitrification and denitrification are the most important with respect to nitrous oxide production. 

The intermediate reactions between sulphoquinovose and sulphoacetaldehyde and the relative contributions of potential intermediates like sulphopyruvate, sulpholactate or sulphoacetate, are unknown at present. The sulphite released would be oxidised either by sulphite oxidases in microorganisms or spontaneously in aerated soils to yield inorganic sulphate, and so provide sulphur for uptake by plants and assimilatory reduction. 

By now it is well established that the assimilatory reduction of nitrate to ammonia proceeds in two separate and well-defined steps (1) The reduction of nitrate to nitrite, catalyzed by the molybdoprotein nitrate reductase, and (2) the reduction of nitrite to ammonia, catalyzed by the heme-protein nitrite reductase ... 

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