Catalyzes the cyanide-resistant oxidation of ubiquinol and the reduction of molecular oxygen to water, but does not translocate protons and consequently is not linked to oxidative phosphorylation. May increase respiration when the cytochrome respiratory pathway is restricted, or in response to low temperatures (By similarity). 2 a ubiquinol + O2 = 2 a ubiquinone + 2 H2O Binds 2 iron ions per subunit. Homodimer; disulfide-linked. Mitochondrial, possibly in the inner surface of the inner mitochondrial membrane. Expressed in roots, seedlings, leaves, flowers and sepals. Highest expression in the senescent leaves. Expressed during early rosette development and during flowering. Up-regulated by antimycin A. No effect of ethylene or cold treatment. Unable to fully compensate for the loss of AOX1A when electron flow via the cytochrome pathway is restricted. Belongs to the alternative oxidase family.