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First published online June 26, 2008; 10.1104/pp.108.123802 Plant Physiology 147:1845-1857 (2008) © 2008 American Society of Plant Biologists OPEN ACCESS ARTICLE
Bridging the Gap between Plant and Mammalian Polyamine Catabolism: A Novel Peroxisomal Polyamine Oxidase Responsible for a Full Back-Conversion Pathway in Arabidopsis1,[W],[OA]Department of Biology, University of Crete, 71409 Heraklion, Greece (P.N.M., A.H.A., K.A.R.-A.); and Centro Nacional de Biotecnologia-Consejo Superior de Investigaciones Científicas, Universidad Autonoma de Madrid, 28049 Madrid, Spain (M.S., E.R., J.J.S.-S.)
In contrast to animals, where polyamine (PA) catabolism efficiently converts spermine (Spm) to putrescine (Put), plants have been considered to possess a PA catabolic pathway producing 1,3-diaminopropane,
1 This work was supported by the National and European resources (EPEAKII-Pythagoras), Greek-Spain Bilateral Agreement, and COST858, COST FA065 Actions; by the Consejo Superior de Investigaciones Científicas I3P Programme cofinanced by the European Social Fund (to M.S.); and by the Onassis Foundation (scholarship to A.H.A.). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Kalliopi A. Roubelakis-Angelakis (poproube{at}biology.uoc.gr). [W] The online version of this article contains Web-only data. [OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.108.123802 * Corresponding author; e-mail poproube{at}biology.uoc.gr. Received May 31, 2008; accepted June 18, 2008; published June 26, 2008. This article has been cited by other articles:
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1-pyrroline, the corresponding aldehyde, and hydrogen peroxide but unable to back-convert Spm to Put. Arabidopsis (Arabidopsis thaliana) genome contains at least five putative PA oxidase (PAO) members with yet-unknown localization and physiological role(s). AtPAO1 was recently identified as an enzyme similar to the mammalian Spm oxidase, which converts Spm to spermidine (Spd). In this work, we have performed in silico analysis of the five Arabidopsis genes and have identified PAO3 (AtPAO3) as a nontypical PAO, in terms of homology, compared to other known PAOs. We have expressed the gene AtPAO3 and have purified a protein corresponding to it using the inducible heterologous expression system of Escherichia coli. AtPAO3 catalyzed the sequential conversion/oxidation of Spm to Spd, and of Spd to Put, thus exhibiting functional homology to the mammalian PAOs. The best substrate for this pathway was Spd, whereas the N1-acetyl-derivatives of Spm and Spd were oxidized less efficiently. On the other hand, no activity was detected when diamines (agmatine, cadaverine, and Put) were used as substrates. Moreover, although AtPAO3 does not exhibit significant similarity to the other known PAOs, it is efficiently inhibited by guazatine, a potent PAO inhibitor. AtPAO3 contains a peroxisomal targeting motif at the C terminus, and it targets green fluorescence protein to peroxisomes when fused at the N terminus but not at the C terminus. These results reveal that AtPAO3 is a peroxisomal protein and that the C terminus of the protein contains the sorting information. The overall data reinforce the view that plants and mammals possess a similar PA oxidation system, concerning both the subcellular localization and the mode of its action. 
