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First published online July 31, 2009
Journal of Experimental Biology 212, 2627-2634 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.032151
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Alternative oxidase in animals: unique characteristics and taxonomic distribution

Allison E. McDonald1,*, Greg C. Vanlerberghe2 and James F. Staples1

1 Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
2 Department of Biological Sciences and Department of Cell and Systems Biology, University of Toronto Scarborough, Toronto, Ontario, Canada M1C 1A4

* Author for correspondence (e-mail: amcdon27{at}uwo.ca)

Accepted 3 June 2009

Alternative oxidase (AOX), a ubiquinol oxidase, introduces a branch point into the respiratory electron transport chain, bypassing complexes III and IV and resulting in cyanide-resistant respiration. Previously, AOX was thought to be limited to plants and some fungi and protists but recent work has demonstrated the presence of AOX in most kingdoms of life, including animals. In the present study we identified AOX in 28 animal species representing nine phyla. This expands the known taxonomic distribution of AOX in animals by 10 species and two phyla. Using bioinformatics we found AOX gene sequences in members of the animal phyla Porifera, Placozoa, Cnidaria, Mollusca, Annelida, Nematoda, Echinodermata, Hemichordata and Chordata. Using reverse-transcriptase polymerase chain reaction (RT-PCR) with degenerate primers designed to recognize conserved regions of animal AOX, we demonstrated that AOX genes are transcribed in several animals from different phyla. An analysis of full-length AOX sequences revealed an amino acid motif in the C-terminal region of the protein that is unique to animal AOXs. Animal AOX also lacks an N-terminal cysteine residue that is known to be important for AOX enzyme regulation in plants. We conclude that the presence of AOX is the ancestral state in animals and hypothesize that its absence in some lineages, including vertebrates, is due to gene loss events.

Key words: mitochondria, cyanide-resistant respiration, animal evolution, sulfide metabolism


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