| Primary Identifier | IPR038659 | Type | Homologous_superfamily |
| Short Name | AOX_sf |
| description | The alternative oxidase (AOX) is an enzyme that forms part of the electron transport chain in mitochondria of different organisms [, ]. Proteins homologous to the mitochondrial oxidase have also been identified in bacterial genomes [, ]. The oxidase provides an alternative route for electrons passing through the electron transport chain to reduce oxygen. However, as several proton-pumping steps are bypassed in this alternative pathway, activation of the oxidase reduces ATP generation. This enzyme was first identified as a distinct oxidase pathway from cytochrome c oxidase as the alternative oxidase is resistant to inhibition by the poison cyanide [].The alternative oxidase (also known as ubiquinol oxidase) is used as a second terminal oxidase in the mitochondria, electrons are transferred directly from reduced ubiquinol to oxygen forming water []. This is not coupled to ATP synthesis and is not inhibited by cyanide, this pathway is a single step process []. In Oryza sativa (rice) the transcript levels of the alternative oxidase are increased by low temperature []. It has been predicted to contain a coupled diiron centre on the basis of aconserved sequence motif consisting of the proposed iron ligands, four Glu and two His residues []. The EPR study of Arabidopsis thaliana (mouse-ear cress) alternative oxidase AOX1a shows that the enzyme contains a hydroxo-bridged mixed-valent Fe(II)/Fe(III) binuclear iron centre []. A catalytic cycle has been proposed that involves a di-iron centre and at least one transient protein-derived radical, most probably an invariant Tyr residue [].The structure of alternative oxidase from Trypanosoma brucei has been solved. The enzyme is a homodimer with the nonhaem di-iron carboxylate active site buried within a four-helix bundle. In the inhibitor-free state, the di-iron carboxylate is ligated by four glutamate residues, but on binding of an inhibitor, a histidine is also induced to act as a ligand. A highly conserved tyrosine is close to the active site and required for activity []. This entry represents proteins with a structure similar to that of alternative oxidase. |
