ALTERNATIVE OXIDASE: From Gene to Function

Abstract

Plants, some fungi, and protists contain a cyanide-resistant, alternative mitochondrial respiratory pathway. This pathway branches at the ubiquinone pool and consists of an alternative oxidase encoded by the nuclear gene Aox1. Alternative pathway respiration is only linked to proton translocation at Complex 1 (NADH dehydrogenase). Alternative oxidase expression is influenced by stress stimuli-cold, oxidative stress, pathogen attack-and by factors constricting electron flow through the cytochrome pathway of respiration. Control is exerted at the levels of gene expression and in response to the availability of carbon and reducing potential. Posttranslational control involves reversible covalent modification of the alternative oxidase and activation by specific carbon metabolites. This dynamic system of coarse and fine control may function to balance upstream respiratory carbon metabolism and downstream electron transport when these coupled processes become imbalanced as a result of changes in the supply of, or demand for, carbon, reducing power, and ATP.

Two Zinc-Cluster Transcription Factors Control Induction of Alternative Oxidase in Neurospora crassa

“…T HE alternative oxidase is found in green plants, many fungi, some protists, some bacteria, and a few animals (Vanlerberghe and Mcintosh 1997;JosephHorne et al 2001;Stenmark and Nordlund 2003;Veiga et al 2003;Vanlerberghe 2004, 2005;Chaudhuri et al 2006). The enzyme catalyzes the transfer of electrons directly from ubiquinol to oxygen, allowing electrons to bypass the final steps of the cytochrome-mediated electron transport chain.…”

Temperature-dependent alterations of respiration in leaves of two selected vascular plant species: the role of the alternative oxidase pathway

“…The role of AOX in vascular plants is still under debate (VANLERBERGHE and MCINTOSH, 1997). It is being discussed if the alternative respiratory pathway can act as one of the important mechanisms acting by chilling acclimatisation (e.g.…”

“…General relations between temperature and respiration are well known (LARCHER, 1995). However, reports on the influence of temperature on the alternative respiratory pathway in vascular plants are really scarce (VANLERBERGHE and MCINTOSH, 1997). A cytochrome pathway (cyanide-sensitive) and an alternative pathway (cyanide-resistant) are considered to be principal parts of the respiratory chain in plant mitochondria.…”

A single amino acid change in the plant alternative oxidase alters the specificity of organic acid activation

“…The latter enzyme catalyses the oxidation of ubiquinol and the reduction of molecular oxygen to water, but does not translocate protons and consequently is not linked to oxidative phosphorylation. Operation of AOX partially deregulates respiration and allows rapid respiration in thermogenic plant tissues and in climacteric fruits [1,2]. However, it is present in all plants so far examined and may play a more general role in cell metabolism by preventing over-reduction of the respiratory chain and production of reactive oxygen intermediates [3 5].…”

“…during thermogenesis or in response to environmental stress such as cold or infection [2]. Often AOX is encoded by a gene family and different genes are regulated in response to different signals [10].…”