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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Heterologous Expression and Biochemical Characterization of a Polyamine Oxidase from Arabidopsis Involved in Polyamine Back Conversion¹

Department of Biology, University Roma Tre, 00146 Rome, Italy (P.T., M.N.R., G.S., F.P., R.A., R.F.); and Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia, Consejo Superior de Investigaciones Científicas, 46022 Valencia, Spain (M.A.P.-A.)

Polyamine oxidase (PAO) is a flavin adenine dinucleotide-dependent enzyme involved in polyamine catabolism. Animal PAOs oxidize spermine (Spm), spermidine (Spd), and/or their acetyl derivatives to produce H₂O₂, an aminoaldehyde, and Spd or putrescine, respectively, thus being involved in a polyamine back-conversion pathway. On the contrary, plant PAOs that have been characterized to date oxidize Spm and Spd to produce 1,3-diaminopropane, H₂O₂, and an aminoaldehyde and are therefore involved in the terminal catabolism of polyamines. A database search within the Arabidopsis (Arabidopsis thaliana) genome sequence showed the presence of a gene (AtPAO1) encoding for a putative PAO with 45% amino acid sequence identity with maize (Zea mays) PAO. The AtPAO1 cDNA was isolated and cloned in a vector for heterologous expression in Escherichia coli. The recombinant protein was purified by affinity chromatography on guazatine-Sepharose 4B and was shown to be a flavoprotein able to oxidize Spm, norspermine, and N¹-acetylspermine with a pH optimum at 8.0. Analysis of the reaction products showed that AtPAO1 produces Spd from Spm and norspermidine from norspermine, demonstrating a substrate oxidation mode similar to that of animal PAOs. To our knowledge, AtPAO1 is the first plant PAO reported to be involved in a polyamine back-conversion pathway.

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: Paraskevi Tavladoraki (tavlador{at}uniroma3.it).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.080911.

^* Corresponding author; e-mail tavlador{at}uniroma3.it; fax 39–06–55176321.

Received March 27, 2006; returned for revision May 15, 2006; accepted May 15, 2006.

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