Alternative oxidase (IPR002680)

Short name: AOX

Overlapping homologous superfamilies

Family relationships



The alternative oxidase (AOX) is an enzyme that forms part of the electron transport chain in mitochondria of different organisms [PMID: 15370881, PMID: 9698817]. Proteins homologous to the mitochondrial oxidase have also been identified in bacterial genomes [PMID: 15082931, PMID: 15087133]. 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 [PMID: 1883834].

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 [PMID: 8770590]. This is not coupled to ATP synthesis and is not inhibited by cyanide, this pathway is a single step process [PMID: 9426242]. In Oryza sativa (rice) the transcript levels of the alternative oxidase are increased by low temperature [PMID: 9426242]. It has been predicted to contain a coupled diiron centre on the basis of a conserved sequence motif consisting of the proposed iron ligands, four Glu and two His residues [PMID: 11106766]. 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 [PMID: 12215444]. 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 [PMID: 11801238].

GO terms

Biological Process

GO:0055114 oxidation-reduction process

Molecular Function

GO:0009916 alternative oxidase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.