Alternative Oxidase (AOX)

The alternative oxidase is an enzyme that forms part of the electron transport chain in plants, as well as some fungi, protists and possibly some animals.Sequences similar to the plant 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 enzyme has been predicted to contain a coupled diiron center on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamine and two histidine amino acid residues.