Nitrite reductase: Difference between revisions
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<StructureSection load='Cca.pdb' size='500' side='right' scene='Journal:JBIC:16/Cv/2' caption=''> | |||
'''Nitrite reductase''' (NIR) catalyzes the reduction of NO2 to NO. There are 2 classes of NIR: (1) A heme-containing cytochrome Cd type NIR. This enzyme contains 4 heme groups. Its d-type heme group binds NO<sub>2</sub>. (2) A copper-containing NIR which produces NO<sub>2</sub>. Under anaerobic conditions bacteria rely on the reduction of nitrogen oxide species to obtain energy. NIR is part of the nitrogen cycle used fot this purpose. | '''Nitrite reductase''' (NIR) catalyzes the reduction of NO2 to NO. There are 2 classes of NIR: (1) A heme-containing cytochrome Cd type NIR. This enzyme contains 4 heme groups. Its d-type heme group binds NO<sub>2</sub>. (2) A copper-containing NIR which produces NO<sub>2</sub>. Under anaerobic conditions bacteria rely on the reduction of nitrogen oxide species to obtain energy. NIR is part of the nitrogen cycle used fot this purpose. | ||
Cytochrome c nitrite reductase (ccNIR) is a central enzyme of the nitrogen cycle. It binds nitrite, and reduces it by transferring 6 electrons to form ammonia. This ammonia can then be utilized to synthesize nitrogen containing molecules such as amino acids or nucleic acids. However, ccNiR’s primary role is to help extract energy from the reduction; ammonia is simply a potentially useful byproduct. In general, heterotrophic organisms feed on electron-rich substances such as sugars or fatty acids. During the metabolism of these substances large numbers of electrons are produced. Many organisms use oxygen as the final acceptor of these electrons, in which case water is formed. However, some organisms can use alternative electron acceptors such as nitrite, which is where ccNiR comes in. | Cytochrome c nitrite reductase (ccNIR) is a central enzyme of the nitrogen cycle. It binds nitrite, and reduces it by transferring 6 electrons to form ammonia. This ammonia can then be utilized to synthesize nitrogen containing molecules such as amino acids or nucleic acids. However, ccNiR’s primary role is to help extract energy from the reduction; ammonia is simply a potentially useful byproduct. In general, heterotrophic organisms feed on electron-rich substances such as sugars or fatty acids. During the metabolism of these substances large numbers of electrons are produced. Many organisms use oxygen as the final acceptor of these electrons, in which case water is formed. However, some organisms can use alternative electron acceptors such as nitrite, which is where ccNiR comes in. | ||
'''Laue Crystal Structure of ''Shewanella oneidensis'' Cytochrome c Nitrite Reductase from a High-yield Expression System''' <ref name="Youngblut">doi 10.1007/s00775-012-0885-0</ref> | '''Laue Crystal Structure of ''Shewanella oneidensis'' Cytochrome c Nitrite Reductase from a High-yield Expression System''' <ref name="Youngblut">doi 10.1007/s00775-012-0885-0</ref> | ||
The ccNiR described here is produced by the ''Shewanella oneidensis'' bacterium, which is remarkable in its own right due to the large number of electron acceptors that it can utilize. ''Shewanella'' is a facultative anaerobe, which means that it will use oxygen if available, but in the absence of oxygen can get rid of its electrons by dumping them on a wide range of alternate acceptors, of which nitrite is only one example. To handle the electron flow ''Shewanella'' uses a large number of promiscuous <scene name='Journal:JBIC:16/Cv/8'>c-heme</scene> containing electron transfer proteins. Indeed, ''Shewanella'' is exceptionally adept at producing c-heme proteins under fast-growth conditions, which many bacteria commonly used for large-scale laboratory gene expression, such as ''E. coli'', are incapable of unless they are first extensively reprogrammed genetically. Since ''Shewanella'' can be easily grown in the lab, and can naturally and easily produce c-hemes, it is an ideal host for generating large quantities of c-heme proteins such as ccNiR. | The ccNiR described here is produced by the ''Shewanella oneidensis'' bacterium, which is remarkable in its own right due to the large number of electron acceptors that it can utilize. ''Shewanella'' is a facultative anaerobe, which means that it will use oxygen if available, but in the absence of oxygen can get rid of its electrons by dumping them on a wide range of alternate acceptors, of which nitrite is only one example. To handle the electron flow ''Shewanella'' uses a large number of promiscuous <scene name='Journal:JBIC:16/Cv/8'>c-heme</scene> containing electron transfer proteins. Indeed, ''Shewanella'' is exceptionally adept at producing c-heme proteins under fast-growth conditions, which many bacteria commonly used for large-scale laboratory gene expression, such as ''E. coli'', are incapable of unless they are first extensively reprogrammed genetically. Since ''Shewanella'' can be easily grown in the lab, and can naturally and easily produce c-hemes, it is an ideal host for generating large quantities of c-heme proteins such as ccNiR. | ||