If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Generation of Precursor Metabolites and Energy → Electron Transfer|
|Generation of Precursor Metabolites and Energy → Respiration → Aerobic Respiration|
Pathway Summary from MetaCyc:
Like fermentation, respiration is a process by which electrons are passed from an electron donor to a terminal electron acceptor. However, in respiration the electrons do not pass directly from the donor to the acceptor. Instead, they pass a number of membrane-bound electron carriers that function as a transport chain, passing the electrons from one to another in steps that follow the electrochemical gradients between the electron donor and the acceptor.
Each oxidized member of the electron transfer chain (which can be a flavoprotein, an electron-transfer-related quinone, a cytochrome, or other type of electron carrier) can be reduced by the reduced form of the preceding member, and the electrons flow through the chain all the way to the terminal acceptor, which could be oxygen in the case of aerobic respiration, or another type of molecule in anaerobic respiration.
Known terminal acceptors include organic compounds (fumarate, dimethyl sulfoxide, or trimethylamine N-oxide), or inorganic compounds (nitrate, nitrite, nitrous oxide, chlorate, perchlorate, oxidized manganese ions, ferric iron, gold, selenate, arsenate, sulfate and elemental sulfur).
During the process of electron transfer, a proton gradient is formed across the membrane due to three potential processes:
1. The use of some of the energy associated with the electron transfer for active pumping of protons out of the cell.
2. Exporting protons out of the cell during electron-to-hydrogen transfers.
3. Scalar reactions that consume protons inside the cell, or produce them outside the cell, without actually moving a proton from one compartment to another.
Upon passage of protons back into the cytoplasm, they drive multisubunit ATP synthase enzymes that generate ATP.
About This Pathway
In the Escherichia coli respiratory chain formed by NADH dehydrogenase I (NDH-1) and cytochrome bo oxidase the transfer of electrons from NADH to cytochrome bo oxidase is coupled to the generation of a proton-motive force across the cytoplasmic membrane.
Four electrons are transferred from the NADH oxidation site to cytochrome bo oxidase by a quinone pool which drives proton translocation in the opposite direction. The number of protons pumped across the membrane by NDH-1 is currently unknown [Yagi03]. However, the H+/e- ratio for NDH-1 is at least 1.5 [Bogachev96]. Cytochrome bo oxidase catalyses both vectorial and scalar proton translocation with both mechanisms contributing a total of eight protons [Puustinen91].
Pathway Evidence Glyph:
Bogachev96: Bogachev AV, Murtazina RA, Skulachev VP (1996). "H+/e- stoichiometry for NADH dehydrogenase I and dimethyl sulfoxide reductase in anaerobically grown Escherichia coli cells." J Bacteriol 178(21);6233-7. PMID: 8892824
Franz07: Franz B, Lichtenberg H, Hormes J, Modrow H, Dahl C, Prange A (2007). "Utilization of solid "elemental" sulfur by the phototrophic purple sulfur bacterium Allochromatium vinosum: a sulfur K-edge X-ray absorption spectroscopy study." Microbiology 153(Pt 4);1268-74. PMID: 17379736
Kita84: Kita K, Konishi K, Anraku Y (1984). "Terminal oxidases of Escherichia coli aerobic respiratory chain. I. Purification and properties of cytochrome b562-o complex from cells in the early exponential phase of aerobic growth." J Biol Chem 1984;259(5);3368-74. PMID: 6365921
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