Ferredoxin nitrite reductase
| Ferredoxin nitrite reductase ( Arabidopsis thaliana ) | ||
|---|---|---|
| Mass / length primary structure | 561 amino acids | |
| Cofactor | Sirohaem , (4Fe-4S) | |
| Identifier | ||
| External IDs | ||
| Enzyme classification | ||
| EC, category | 1.7.7.1 , Oxidoreductase | |
| Response type | Redox reaction | |
| Substrate | NO 2 - + 6 Ferredoxin red. + 8 H + | |
| Products | NH 4 + + 6 ferredoxin ox. + 2 H 2 O | |
| Occurrence | ||
| Parent taxon | Plants , algae , cyanobacteria | |
The ferredoxin-nitrite reductase (NiR) is an enzyme in plants, algae and cyanobacteria , which in the plastids is localized and nitrite to ammonium reduced . This is a reaction step in the metabolic pathway of nitrate assimilation , in which the nitrogen supplied, for example, by nitrate fertilization , is made available to the plant as ammonium ion.
The catalyzed reaction:
NiR is one of the nitrite reductases . Homologous enzymes in bacteria are able to reduce sulfite .
Importance of nitrite reductase in the plant organism
Plants absorb nitrogen in the form of nitrate (NO 3 - ) or ammonium (NH 4 + ) from the water or the soil. Nitrogen absorbed in the form of nitrate must be converted into ammonium in order to be available for synthesis of organic material. The first step in nitrate reduction is catalyzed by nitrate reductase . The nitrate reductase reduces nitrate to nitrite (NO 2 - ). In a second step, nitrite is then further reduced to ammonium, which catalyzes the nitrite reductase .
Nitrite is a cell poison and must therefore be converted quickly. Since u. a. the affinity of the nitrite reductase for nitrite is high, the nitrite formed by the nitrate reductase is completely converted.
biochemistry
The vegetable nitrite reductase is nucleus-coded , but only localized in the plastids . In contrast to the nitrate reduction in the cytosol , the nitrite reduction takes place in the plastids.
The enzyme has two covalently bound cofactors : a (4Fe-4S) iron-sulfur cluster and a siroheme . The cofactors form an electron transport chain and transfer electrons from the electron donor ferredoxin to the nitrite. Six electrons have to be transferred for a complete reduction of the nitrite:
The electrons come mainly from photosynthesis ( photosystem I), which reduce oxidized ferredoxin again. Alternatively, smaller amounts of ferrodoxine can also be reduced using NADPH . The plant in the roots depends on this, since photosynthesis cannot take place there.
Individual evidence
- ↑ Homologues at OMA .
- ↑ Hans W. Heldt and Birgit Piechulla: Plant biochemistry . Spectrum Akademischer Verlag GmbH, 4th edition 2008; ISBN 978-3-8274-1961-3 ; P. 267 f.
- ↑ EC 1.7.7.1 (nitrite reductase).
- ↑ Hans W. Heldt and Birgit Piechulla: Plant biochemistry . Spectrum Akademischer Verlag GmbH, 4th edition 2008; ISBN 3-8274-1330-3 ; P. 267.
literature
- Magalhaes, AC. et al. (1974): Nitrite Assimilation and Amino Nitrogen Synthesis in Isolated Spinach Chloroplasts . In: Plant Physiol. 53 (3); 411-415; PMID 16658715 ; PDF (free full text access)