Plant Phenylacetaldehyde Synthase Is a Bifunctional Homotetrameric Enzyme That Catalyzes Phenylalanine Decarboxylation and Oxidation

Yasuhisa Kaminaga,Jennifer Schnepp,Greg Peel,Christine M Kish,Gili Ben-Nissan,David Weiss,Irina Orlova,Orly Lavie,David Rhodes,Karl Wood,D Marshall Porterfield,Arthur J.L Cooper,John V Schloss,Eran Pichersky,Alexander Vainstein,Natalia Dudareva

doi:10.1074/jbc.m602708200

Abstract

We have isolated and characterized Petunia hybrida cv. Mitchell phenylacetaldehyde synthase (PAAS), which catalyzes the formation of phenylacetaldehyde, a constituent of floral scent. PAAS is a cytosolic homotetrameric enzyme that belongs to group II pyridoxal 5'-phosphate-dependent amino-acid decarboxylases and shares extensive amino acid identity (approximately 65%) with plant L-tyrosine/3,4-dihydroxy-L-phenylalanine and L-tryptophan decarboxylases. It displays a strict specificity for phenylalanine with an apparent Km of 1.2 mM. PAAS is a bifunctional enzyme that catalyzes the unprecedented efficient coupling of phenylalanine decarboxylation to oxidation, generating phenylacetaldehyde, CO2, ammonia, and hydrogen peroxide in stoichiometric amounts.

Highlights

Aldehydes are intermediates in a variety of biochemical pathways, including those involved in the metabolism of carbohydrates, vitamins, steroids, amino acids, benzylisoquinoline alkaloids, hormones, and lipids [1, 2]
Occurrence of Oxidative Decarboxylation Catalyzed by PLPdependent Decarboxylases—Native pig kidney dihydroxyphenylalanine decarboxylase (DDC) [44, 47], E. coli glutamate decarboxylase [43, 52], and Lactobacillus 30a ornithine decarboxylase [52] can catalyze the oxidative decarboxylation of ␣-methyl-Dopa, ␣-methylglutamate, and ␣-methylornithine, respectively
There is ample precedent for the present finding that a PLP-dependent decarboxylase such as phenylacetaldehyde synthase (PAAS) can catalyze the oxidative decarboxylation of its ␣-methylamino acid analog

Summary

Plant Phenylacetaldehyde Synthase Is a Bifunctional

Aldehydes are intermediates in a variety of biochemical pathways, including those involved in the metabolism of carbohydrates, vitamins, steroids, amino acids, benzylisoquinoline alkaloids, hormones, and lipids [1, 2] In plants, they are synthesized in response to environmental stresses such as salinity, cold, and heat shock [3, 4] or as flavors and aromas in fruits and flowers [5, 6]. We describe the isolation of a cDNA encoding phenylacetaldehyde synthase (PAAS) and the biochemical characterization of the recombinant protein, which catalyzes an unusual, combined decarboxylation-amine oxidation reaction, leading to the formation of PHA from Phe. Plant Phenylacetaldehyde Synthase nitrilotriacetic acid-agarose (0.5-ml bed volume). The eluate fractions (1 ml each) with the highest PAAS

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION