Function of the alternative oxidase: is it still a scavenger?

Moore, Anthony L.; Albury, Mary S.; Crichton, Paul G.; Affourtit, Charles

doi:10.1016/s1360-1385(02)02366-x

Cited by 174 publications

(118 citation statements)

References 20 publications

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“…Although its function in non-thermogenic plants is less well understood, AOX may serve to allow the continued operation of upstream carbon metabolism (glycolysis and the tricarboxylic acid cycle) when the cytochrome chain is inhibited by specific stress factors or otherwise restricted by high cellular ATP/ADP ratio . By providing a second pathway of electron flow, AP respiration may also serve to prevent the over-reduction of electron transport components, particularly the ubiquinone pool, which would exacerbate the formation of damaging reactive oxygen species (ROS) (see Møller 2001, Moore et al 2002. Excessive mitochondrial ROS formation is seen as an indicator of mitochondrial dysfunction (Raha and Robinson 2000) and is a key trigger of programmed cell death (Lam et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Characterization of the alternative oxidase of Chlamydomonas reinhardtii in response to oxidative stress and a shift in nitrogen source

Molen

Rosso

Piercy

et al. 2006

Physiologia Plantarum

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To study the transcriptional regulation of Aox1, the major alternative oxidase (AOX) gene, we fused 1072 bp of its promoter to the promoterless arylsulfatase reporter gene. We find that the reporter is strongly activated when cells are shifted from a medium containing ammonium to one containing nitrate but is unresponsive to treatments known to induce Aox1 in higher plants -H 2 O 2 , antimycin A and cold stress. However, induction of Aox1 by all these factors was found when changes in gene expression were monitored using RNA blot analysis. Our data suggest that transcriptional upregulation of Aox1 by H 2 O 2 , antimycin A and cold-stress requires one or more enhancers which are not found in the proximal promoter region of the gene. Interestingly, while nitrate, H 2 O 2 and cold stress result in increased AOX abundance and increased alternative pathway respiration, these changes are not seen when cells are treated with antimycin A. We find that H 2 O 2 , antimycin A and cold-stress result in an increase in intracellular reactive oxygen species (ROS) but that a significant change in ROS does not occur when cells are shifted into a medium-containing nitrate. Overall, our data are consistent with there being two distinct pathways regulating Aox1 transcription and AOX abundance in Chlamydomonas reinhardtii: one in response to oxidative stress and a second due to metabolic changes brought about by a shift in nitrogen source from ammonium to nitrate.

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Section: Introductionmentioning

confidence: 99%

Characterization of the alternative oxidase of Chlamydomonas reinhardtii in response to oxidative stress and a shift in nitrogen source

Molen

Rosso

Piercy

et al. 2006

Physiologia Plantarum

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“…In thermogenic plants this alternative oxidase (AOX) 6 plays a key role in the release of heat for pollination purposes or for maintaining a warm environment within the flower at low ambient temperatures. In nonthermogenic plants its function is still under debate; proposed roles include maintaining tricarboxylic acid cycle turnover under high cytosolic phosphorylation potentials, defense against oxidative stress, and growth rate and energy charge homeostasis (4). AOX is also found in species of fungi, green algae, bacteria, and protozoa (5) and, more recently, in mollusks, nematodes, and chordates (6).…”

mentioning

confidence: 99%

Three Redox States of Trypanosoma brucei Alternative Oxidase Identified by Infrared Spectroscopy and Electrochemistry

Maréchal

Kido

Kita

et al. 2009

Journal of Biological Chemistry

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Electrochemistry coupled with Fourier transform infrared (IR) spectroscopy was used to investigate the redox properties of recombinant alternative ubiquinol oxidase from Trypanosoma brucei, the organism responsible for African sleeping sickness.Stepwise reduction of the fully oxidized resting state of recombinant alternative ubiquinol oxidase revealed two distinct IR redox difference spectra. The first of these, signal 1, titrates in the reductive direction as an n ‫؍‬ 2 Nernstian component with an apparent midpoint potential of 80 mV at pH 7.0. However, reoxidation of signal 1 in the same potential range under anaerobic conditions did not occur and only began with potentials in excess of 500 mV. Reoxidation by introduction of oxygen was also unsuccessful. Signal 1 contained clear features that can be assigned to protonation of at least one carboxylate group, further perturbations of carboxylic and histidine residues, bound ubiquinone, and a negative band at 1554 cm ؊1 that might arise from a radical in the fully oxidized protein. A second distinct IR redox difference spectrum, signal 2, appeared more slowly once signal 1 had been reduced. This component could be reoxidized with potentials above 100 mV. In addition, when both signals 1 and 2 were reduced, introduction of oxygen caused rapid oxidation of both components. These data are interpreted in terms of the possible active site structure and mechanism of oxygen reduction to water.Mitochondria from many higher plants possess, in addition to the conventional cytochrome c oxidase, a second terminal oxidase that oxidizes ubiquinol (1-3). In thermogenic plants this alternative oxidase (AOX) 6 plays a key role in the release of heat for pollination purposes or for maintaining a warm environment within the flower at low ambient temperatures. In nonthermogenic plants its function is still under debate; proposed roles include maintaining tricarboxylic acid cycle turnover under high cytosolic phosphorylation potentials, defense against oxidative stress, and growth rate and energy charge homeostasis (4). AOX is also found in species of fungi, green algae, bacteria, and protozoa (5) and, more recently, in mollusks, nematodes, and chordates (6). Of particular importance, however, is its presence in pathogenic protozoa such as the blood parasite Trypanosoma brucei (7) and the intestinal parasite Cryptosporidium parvum (8, 9). T. brucei is a parasite that causes African sleeping sickness in humans and Nagana in livestock and is transmitted by the tsetse fly (7). The bloodstream forms of T. brucei appear to depend solely on its alternative oxidase (TAO) for respiration. Because the protein is absent from the mammalian host, TAO is an attractive and important chemotherapeutic target for African trypanosomiasis (7-10). In this respect it is interesting to note that ascofuranone, isolated from the pathogenic fungus Ascochyta visiae, specifically and potently inhibits the quinol oxidase activity of TAO (11) and rapidly kills the parasites. In addition, the chemotherapeutic eff...

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“…For example, in plants the enzyme may prevent the accumulation of reactive oxygen species, prevent programmed cell death, and/or ensure proper energy and biosynthetic balance during growth (Maxwell et al 1999;Hansen et al 2002;Moore et al 2002;Robson and Vanlerberghe 2002;Vanlerberghe et al 2002;Sieger et al 2005;Umbach et al 2005;Ho et al 2007). The best-defined function of alternative oxidase is in certain plant species where the heat generated via the alternative pathway of electron transport is used to volatilize aromatic compounds that attract insect pollinators (Vanlerberghe and McIntosh 1997).…”

mentioning

confidence: 99%

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

Chae

Nargang

Cleary³

et al. 2007

Genetics

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The alternative oxidase transfers electrons from ubiquinol to molecular oxygen, providing a mechanism for bypassing the later steps of the standard cytochrome-mediated electron transport chain. The enzyme is found in an array of organisms and in many cases is known to be produced in response to perturbations of the standard chain. Alternative oxidase is encoded in the nucleus but functions in the inner mitochondrial membrane. This implies the existence of a retrograde regulation pathway for communicating from the mitochondrion to the nucleus to induce alternative oxidase expression. Previous studies on alternative oxidase in fungi and plants have shown that a number of genes are required for expression of the enzyme, but the identity of these genes has remained elusive. By gene rescue we have now shown that the aod-2 and aod-5 genes of Neurospora crassa encode transcription factors of the zinc-cluster family. Electrophoretic mobility shift assays show that the DNA-binding domains of the AOD2 and AOD5 proteins act in tandem to bind a sequence element in the alternative oxidase gene promoter that is required for expression. Both proteins contain potential PAS domains near their C terminus, which are found primarily in proteins involved in signal transduction.

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Function of the alternative oxidase: is it still a scavenger?

Cited by 174 publications

References 20 publications

Characterization of the alternative oxidase of Chlamydomonas reinhardtii in response to oxidative stress and a shift in nitrogen source

Characterization of the alternative oxidase of Chlamydomonas reinhardtii in response to oxidative stress and a shift in nitrogen source

Three Redox States of Trypanosoma brucei Alternative Oxidase Identified by Infrared Spectroscopy and Electrochemistry

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

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