EC Number   |
Substrates |
Organism |
Products |
Reversibility |
|---|
   1.7.5.1 | more |
Escherichia coli expresses two different membrane-bound respiratory nitrate reductases, nitrate reductase A (NRA) and nitrate reductase Z (NRZ). The two enzymes are encoded by distinct operons located within two different loci on the Escherichia coli chromosome. The narGHJI operon, encoding nitrate reductase A, is located in the chlC locus at 27 min, along with several functionally related genes: narK, encoding a nitrate/nitrite antiporter, and the narXL operon, encoding a nitrate-activated, two component regulatory system. The narZYWV operon, encoding nitrate reductase Z, is located in the chlZ locus located at 32.5 min, a region which includes a narK homologue, narU, but no apparent homologue to the narXL operon. The two membrane-bound enzymes have similar structures and biochemical properties and are capable of reducing nitrate using normal physiological substrates. The homology of the amino acid sequences of the peptides encoded by the two operons is extremely high but the intergenic regions share no related sequences. The expression of both the narGHJI operon and the narK gene are positively regulated by two transacting factors Fnr and NarL-phosphate, activated respectively by anaerobiosis and nitrate, while the narZYWV operon and the narU gene are constitutively expressed. Nitrate reductase A, which accounts for 98% of the nitrate reductase activity when fully induced, is clearly the major respiratory nitrate reductase in Escherichia coli |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | more |
nitrate reductase Z expression is regulated in a manner opposite to that of nitrate reductase A. The narGHJZ operon is aerobically repressed, strongly induced by nitrate and positively regulated by the fnr gene product. The expression of narZ is anaerobically repressed, induced weakly, if at all, by nitrate and negatively regulated by the fnr gene product. The opposing regulation of these two enzymes suggests that a function of nitrate reductase Z may be to catalyse the immediate flow of electrons to nitrate during an aerobic/anaerobic transition when the bacterium is grown in the presence of nitrate |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | more |
nitrate reductase Z is synthesized in small amounts, the expression of its structural genes does not seem to be induced by nitrate, repressed by oxygen or activated by the product of the fnr gene. The nitrate reductase Z in mutant LCB79/pLCB14 couples formate oxidation with nitrate reduction probably via quinones and type-b cytochromes |
Escherichia coli K-12 |
? |
- |
? |
| 1.7.5.1 | more |
NRZ is expressed at a low level that is not influenced by anaerobiosis or nitrate. The NRZ operon is controlled mainly at the level of transcription and is induced 10fold at the onset of stationary phase in rich media. Expression of NRZ nitrate reductase is highly growth phase dependent and is controlled by the alternative vegetative sigma factor RpoS. RpoS-mediated regulation of NRZ may be an important physiological adaptation that allows the cell to use nitrate under stress-associated conditions |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | more |
bromate and chlorate are substrates of the enzyme |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | more |
nitrate reductase Z is able to use both nitrate and chlorate as substrate |
Escherichia coli K-12 |
? |
- |
? |
| 1.7.5.1 | more |
the holoenzyme has two independent and spatially distinct active sites, one for quinol oxidation and the other for nitrate reduction |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | more |
structure-function relationships of quinone reactivity |
Escherichia coli |
? |
- |
? |
| 1.7.5.1 | nitrate + 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinol |
i.e. decylubiquinol |
Escherichia coli |
nitrite + 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone + H2O |
- |
? |
| 1.7.5.1 | nitrate + 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinol |
- |
Escherichia coli |
nitrite + 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone + H2O |
- |
? |
