Irina Orlova

Volatile compounds act as a language that plants use for their communication and interaction with the surrounding environment. To date, a total of 1700 volatile compounds have been isolated from more than 90 plant families. These volatiles, released from leaves, flowers, and fruits into the atmosphere and from roots into the soil, defend plants against herbivores and pathogens or provide a reproductive advantage by attracting pollinators and seed dispersers. Plant volatiles constitute about 1% of plant secondary metabolites and are mainly represented by terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. In this review we focus on the functions of plant volatiles, their biosynthesis and regulation, and the metabolic engineering of the volatile spectrum, which results in plant defense improvement and changes of scent and aroma properties of flowers and fruits.

Terpenoids, the largest class of plant secondary metabolites, play essential roles in both plant and human life. In higher plants, the five-carbon building blocks of all terpenoids, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate, are derived from two independent pathways localized in different cellular compartments. The methylerythritol phosphate (MEP or nonmevalonate) pathway, localized in the plastids, is thought to provide IPP and dimethylallyl diphosphate for hemiterpene, monoterpene, and diterpene biosynthesis, whereas the cytosol-localized mevalonate pathway provides C5 units for sesquiterpene biosynthesis. Stable isotope-labeled, pathway-specific precursors (1-deoxy-[5,5-2H2]-D-xylulose and [2,2-2H2]-mevalolactone) were supplied to cut snapdragon flowers, which emit both monoterpenes and the sesquiterpene, nerolidol. We show that only one of the two pathways, the plastid-localized MEP pathway, is active in the formation of volatile terpenes. The MEP pathway provides IPP precursors for both plastidial monoterpene and cytosolic sesquiterpene biosynthesis in the epidermis of snapdragon petals. The trafficking of IPP occurs unidirectionally from the plastids to cytosol. The MEP pathway operates in a rhythmic manner controlled by the circadian clock, which determines the rhythmicity of terpenoid emission.

In vivo stable isotope labeling and computer-assisted metabolic flux analysis were used to investigate the metabolic pathways in petunia (Petunia hybrida) cv Mitchell leading from Phe to benzenoid compounds, a process that requires the shortening of the side chain by a C(2) unit. Deuterium-labeled Phe ((2)H(5)-Phe) was supplied to excised petunia petals. The intracellular pools of benzenoid/phenylpropanoid-related compounds (intermediates and end products) as well as volatile end products within the floral bouquet were analyzed for pool sizes and labeling kinetics by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. Modeling of the benzenoid network revealed that both the CoA-dependent, beta-oxidative and CoA-independent, non-beta-oxidative pathways contribute to the formation of benzenoid compounds in petunia flowers. The flux through the CoA-independent, non-beta-oxidative pathway with benzaldehyde as a key intermediate was estimated to be about 2 times higher than the flux through the CoA-dependent, beta-oxidative pathway. Modeling of (2)H(5)-Phe labeling data predicted that in addition to benzaldehyde, benzylbenzoate is an intermediate between l-Phe and benzoic acid. Benzylbenzoate is the result of benzoylation of benzyl alcohol, for which activity was detected in petunia petals. A cDNA encoding a benzoyl-CoA:benzyl alcohol/phenylethanol benzoyltransferase was isolated from petunia cv Mitchell using a functional genomic approach. Biochemical characterization of a purified recombinant benzoyl-CoA:benzyl alcohol/phenylethanol benzoyltransferase protein showed that it can produce benzylbenzoate and phenylethyl benzoate, both present in petunia corollas, with similar catalytic efficiencies.

Phenylpropenes such as chavicol, t-anol, eugenol, and isoeugenol are produced by plants as defense compounds against animals and microorganisms and as floral attractants of pollinators. Moreover, humans have used phenylpropenes since antiquity for food preservation and flavoring and as medicinal agents. Previous research suggested that the phenylpropenes are synthesized in plants from substituted phenylpropenols, although the identity of the enzymes and the nature of the reaction mechanism involved in this transformation have remained obscure. We show here that glandular trichomes of sweet basil (Ocimum basilicum), which synthesize and accumulate phenylpropenes, possess an enzyme that can use coniferyl acetate and NADPH to form eugenol. Petunia (Petunia hybrida cv. Mitchell) flowers, which emit large amounts of isoeugenol, possess an enzyme homologous to the basil eugenol-forming enzyme that also uses coniferyl acetate and NADPH as substrates but catalyzes the formation of isoeugenol. The basil and petunia phenylpropene-forming enzymes belong to a structural family of NADPH-dependent reductases that also includes pinoresinol-lariciresinol reductase, isoflavone reductase, and phenylcoumaran benzylic ether reductase.

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 (∼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. 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 (∼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. 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 (1Yoshida A. Rzhetsky A. Hsu L.C. Chang C. Eur. J. Biochem. 1998; 251: 549-557Crossref PubMed Scopus (394) Google Scholar, 2Seo M. Akaba S. Oritani T. Delarue M. Bellini C. Caboche M. Koshiba T. Plant Physiol. 1998; 116: 687-693Crossref PubMed Scopus (150) Google Scholar). In plants, they are also synthesized in response to environmental stresses such as salinity, cold, and heat shock (3Bartels D. Trends Plant Sci. 2001; 6: 284-286Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar, 4Barclay K.D. McKersies B.D. Lipids. 1994; 29: 877-882Crossref PubMed Scopus (58) Google Scholar) or as flavors and aromas in fruits and flowers (5Knudsen J.T. Tollsten L. Bergstrom G. Phytochemistry. 1993; 33: 253-280Crossref Scopus (814) Google Scholar, 6Buttery R.G. Acree T.E. Teranshi R. Flavor Science: Sensible Principles and Techniques. American Chemical Society, Washington, D. C.1993Google Scholar). For example, phenylacetaldehyde (PHA), 2The abbreviations used are: PHA, phenylacetaldehyde; PAAS, phenylacetaldehyde synthase; PLP, pyridoxal 5′-phosphate; GC-MS, gas chromatography-mass spectrometry; l-Dopa, 3,4-dihydroxy-l-phenylalanine; TYDC, l-tyrosine/3,4-dihydroxy-l-phenylalanine decarboxylase; PMP, pyridoxamine 5′-phosphate; DDC, 3,4-dihydroxyphenylalanine decarboxylase. 2-phenylethanol, and its acetate ester are important scent compounds in numerous flowers (5Knudsen J.T. Tollsten L. Bergstrom G. Phytochemistry. 1993; 33: 253-280Crossref Scopus (814) Google Scholar), including petunias (7Verdonk J.C. de Vos C.H.R. Verhoeven H.A. Haring M.A. van Tunen A.J. Schuurink R.C. Phytochemistry. 2003; 62: 997-1008Crossref PubMed Scopus (218) Google Scholar, 8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar) and roses (9Shalit M. Shafir S. Larkov O. Bar E. Kaslassi D. Adam Z. Zamir D. Vainstein A. Weiss D. Ravid U. Lewinsohn E. Isr. J. Plant Sci. 2004; 52: 245-255Crossref Scopus (28) Google Scholar). They also contribute to the aromas of tomato (6Buttery R.G. Acree T.E. Teranshi R. Flavor Science: Sensible Principles and Techniques. American Chemical Society, Washington, D. C.1993Google Scholar), grape (10Garcia E. Chacon J.L. Martinez J. Izquierdo P.M. Food Sci. Technol. Int. 2003; 9: 33-41Crossref Scopus (92) Google Scholar), and tamarind (11Pino J.A. Marbot R. Vazquez C. J. Essent. Oil Res. 2004; 16: 318-320Crossref Scopus (20) Google Scholar) fruits and to the flavor of tea (12Ravichandran R. Parthiban R. Food Chem. 1998; 62: 347-353Crossref Scopus (75) Google Scholar). PHA has been identified in some animals and fungi as well (13Deml R. Dettner K. Entomol. Gen. 1995; 19: 239-252Crossref Scopus (9) Google Scholar, 14Vuralhan Z. Morais M.A. Tai S.L. Piper M.D.W. Pronk J.T. Appl. Environ. Microbiol. 2003; 69: 4534-4541Crossref PubMed Scopus (153) Google Scholar). PHA, 2-phenylethanol, and phenylethyl acetate each contain a benzene ring with a 2-carbon side chain and are therefore referred to as C-6–C-2 compounds. The synthesis of PHA in yeast proceeds from l-phenylalanine to phenylpyruvate via transamination followed by decarboxylation (14Vuralhan Z. Morais M.A. Tai S.L. Piper M.D.W. Pronk J.T. Appl. Environ. Microbiol. 2003; 69: 4534-4541Crossref PubMed Scopus (153) Google Scholar, 15Dickinson J.R. Eshantha L. Salgado J. Hewlins M.J.E. J. Biol. Chem. 2003; 278: 8028-8034Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar). Hazen et al. (16Hazen S.L. d'Avignon A. Anderson M.M. Hsu F.F. Heinecke J.W. J. Biol. Chem. 1998; 273: 4997-5005Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar) postulated that oxidative decarboxylation of Phe by the myeloperoxidase-hydrogen peroxide-chlorine system can also lead to PHA. However, little is known about the biosynthesis of volatile C-6–C-2 compounds in plants. Feeding of petunia petals with deuterium (2H5)-labeled Phe results in a PHA labeling pattern consistent with synthesis from Phe via negligible pools of intermediates (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). Moreover, 2-aminoindane phosphonate, a specific inhibitor of l-phenylalanine ammonia-lyase (EC 4.3.1.5), does not inhibit PHA synthesis but instead increases it by ∼2-fold, suggesting that the formation of PHA from Phe does not occur via trans-cinnamic acid and is in competition with trans-cinnamic acid synthesis for Phe utilization (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). Similar labeling experiments were carried out with [2H8]Phe to determine the route to PHA and subsequent phenylethanol biosynthesis in rose petals (17Watanabe S. Hayashi K. Yagi K. Asai T. MacTavish H. Picone J. Turnbull C. Watanabe N. Biosci. Biotechnol. Biochem. 2002; 66: 943-947Crossref PubMed Scopus (47) Google Scholar, 18Hayashi S. Yagi K. Ishikawa T. Kawasaki M. Asai T. Picone J. Turnbull C. Hiratake J. Sakata K. Takada M. Ogawa K. Watanabe N. Tetrahedron. 2004; 60: 7005-7013Crossref Scopus (31) Google Scholar). A mixture of PHA isotopomers differing in hydrogen labeling (2Hor 1H) at C-1 was obtained. The occurrence of two competing pathways to PHA synthesis, one via the decarboxylation of Phe to 2-phenylethylamine followed by amine oxidation and the second via deamination of Phe to phenylpyruvate followed by its decarboxylation, as occurs in yeast, was suggested (17Watanabe S. Hayashi K. Yagi K. Asai T. MacTavish H. Picone J. Turnbull C. Watanabe N. Biosci. Biotechnol. Biochem. 2002; 66: 943-947Crossref PubMed Scopus (47) Google Scholar, 18Hayashi S. Yagi K. Ishikawa T. Kawasaki M. Asai T. Picone J. Turnbull C. Hiratake J. Sakata K. Takada M. Ogawa K. Watanabe N. Tetrahedron. 2004; 60: 7005-7013Crossref Scopus (31) Google Scholar). These two postulated pathways are shown in Fig. 1. However, to date, no enzyme activities have been demonstrated for either of the postulated pathways in plants. Here, 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 Material—Petunia hybrida cv. Mitchell plants (Ball Seed, West Chicago, IL) were grown under standard green-house conditions (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). Labeling experiments were performed as described previously using corolla limbs of 2-day-old petunia flowers (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar), and emitted volatiles were collected by a closed-loop stripping method over 4 h during the day (19Donath J. Boland W. Phytochemistry. 1995; 39: 785-790Crossref Scopus (104) Google Scholar). Radiolabeled- and Stable Isotope-labeled Compounds—Deuterium-labeled l-phenylalanine (C6D5CD2CD(NH2)COOH; l-[2H8]Phe) was purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA), and l-[U-14C]Tyr (434 mCi/mmol) from Amersham Biosciences. l-[U-14C]Phe (425 mCi/mmol) and sodium [14C]bicarbonate (53 mCi/mmol) were purchased from American Radiolabeled Chemicals, Inc. (St. Louis, MO). Other Reagents—All other reagents were purchased from Sigma or Aldrich. Expression of PAAS in Escherichia coli and Purification of Recombinant Protein—The coding region of petunia PAAS was amplified by PCR using forward and reverse primers (5′-ATTCATATGGATACTATCAAAATCAACCC-3′ and 5′-GGGATCCTTCTACGCATTCAGCATCATAG-3′, respectively) and subcloned into the expression vector pET-28a containing an N-terminal hexahistidine tag (Novagen, Madison, WI). The forward and reverse primers for rose PAAS were 5′-GCCCATGGGTAGCTTCCCATTCCA-3′ and 5′-GGATCCTCAATACGTGCTGAGGATTGG-3′, respectively. Sequencing revealed no errors introduced during PCR amplifications. For functional expression, E. coli BL21 Rosetta competent cells were transformed with the resulting recombinant plasmid and the pET vector without an insert as a control and grown in LB medium with 50 μg/ml at and by were performed as described previously F. N. J. Kish C.M. Dudareva N. Biochem. 2002; PubMed Scopus Google Scholar) with the the expression of PAAS was by the of to a of mm. a with at the E. coli cells were by and in containing sodium pyridoxal and The cells were with for followed by a of the by for at the enzyme in the was by The was with containing sodium and the of the from the was that of the The was from the with of the containing The with the PAAS were into PLP, and with the PAAS were by followed by of the The of the isolated was and Fig. The of the enzyme was into for of the of and for of PAAS and standard mixture PAAS and l-[U-14C]Phe in containing 50 PLP, and for at the was with of The was with of and of the was in a The were to the specific of the and of were by the method of M.M. Biochem. PubMed Scopus Google Scholar) using the and as a was performed by and gas chromatography-mass For 50 of the was a and with compounds as using as a For the enzyme was to and or of and and were in at using a and for For the mixture of PLP, and 4 of PAAS of and of coupling and of J.L. S.L. Lipids. 1993; PubMed Scopus Google Scholar). The at was at and the of was by to in the The of was using The standard mixture of of containing 50 PLP, and 4 of Laboratories, and of PAAS of The in at was at and from a Phe. The of was using the of The of was by Plant Physiol. PubMed Scopus Google Scholar). at were performed in a with and of and enzyme were performed in a were by with an that such as from the of the which was to an were by of a and at a The was from a The were and the and was by The of was by the in in the mixture with was to the method of and H. J. Biol. Chem. Full Text PDF PubMed Google Scholar). and was isolated from petunia floral petals at of and at during a and as described previously (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). A containing the coding region of the PAAS was used as a and of PAAS Petunia of the PAAS by PCR with primers and was into P.M. Sci. U. S. A. 1998; PubMed Scopus Google Scholar) to the in the and by an The was in the vector by and of were performed as described Tunen A.J. J. PubMed Scopus Google Scholar). volatiles were collected from petunia flowers and by as described previously N. M. I. Bar E. T. N. Shafir S. Zamir D. Adam Z. Vainstein A. Weiss D. E. Lewinsohn E. Plant Physiol. 2002; PubMed Scopus Google Scholar). and Expression of Petunia and tag for hybrida cv. Mitchell (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar) and rose I. M. N. D. M. G. Bar E. O. M. M. J. Adam Z. E. Lewinsohn E. Zamir D. Vainstein A. Weiss D. Plant 2002; PubMed Scopus Google Scholar) were for involved in PHA including and amine and two one amine one and one l-tyrosine/3,4-dihydroxy-l-phenylalanine for revealed that the petunia and rose PAAS to TYDC, expression and with the of PHA in petunia and in rose flowers for rose not (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar, I. M. N. D. M. G. Bar E. O. M. M. J. Adam Z. E. Lewinsohn E. Zamir D. Vainstein A. Weiss D. Plant 2002; PubMed Scopus Google Scholar). of petunia with PAAS expression no PHA with These plants also no that PHA is a of (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). Petunia PAAS a of amino with a of and of belongs to group II amino-acid including and decarboxylases E. Eur. J. Biochem. 1994; PubMed Scopus (218) Google Scholar). It shares amino acid identity with from J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar), and H. K. D. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar) and is to l-tryptophan decarboxylases (EC from M. Plant J. PubMed Scopus Google Scholar) and D. R. J. Plant Biol. PubMed Scopus Google Scholar) PAAS a of and is to petunia petunia rose PAAS at its suggesting cytosolic of Recombinant Petunia petunia and rose PAAS in E. coli were with amino acids, including l-Dopa, and as strict specificity for and the of by was PHA A and shown for petunia characterization of recombinant petunia PAAS revealed an apparent Km for Phe of which is to the Km of for and to Phytochemistry. 1995; PubMed Scopus Google Scholar). In 2-day-old petunia the of Phe at is (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar), which to a of a that is the PAAS Km for Phe of 1.2 mm. The PAAS was was at The of petunia PAAS by was suggesting that the enzyme is a containing l-tryptophan and were to Phytochemistry. PubMed Scopus Google Scholar), a was for from D. I. G. K. G. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) and from S. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The of during and in a of enzyme However, the of in the followed by and in the of in a of PAAS The of the in a that PAAS is a The for was The and PAAS and or it by The PAAS an at consistent with the of a The in PAAS was of PAAS or of PAAS as by the method H. J. Biol. Chem. Full Text PDF PubMed Google Scholar). A of 1.2 of of was for D. I. G. K. G. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). from a variety of plants are to l-phenylalanine ammonia-lyase Phytochemistry. PubMed Scopus Google Scholar). a with l-phenylalanine ammonia-lyase N. J. PubMed Scopus Google Scholar), PAAS by 2-aminoindane a l-phenylalanine ammonia-lyase inhibitor J. N. Chem. 6: Scopus Google Scholar), PAAS by The was consistent with that 2-aminoindane of petunia petals does not inhibit PHA (8Boatright J. Negre F. Chen X. Kish C.M. Wood B. Peel G. Orlova I. Gang D. Rhodes D. Dudareva N. Plant Physiol. 2004; 135: 1993-2011Crossref PubMed Scopus (335) Google Scholar). of PHA from Phe via one of at which an acid followed by decarboxylation, resulting in the formation of PHA, CO2, and the amino with phenylpyruvate as an decarboxylation followed by oxidative which results in the formation of PHA, CO2, ammonia, and the of the deamination with 2-phenylethylamine as an oxidative deamination of Phe followed by decarboxylation, leading to the formation of the as in but with phenylpyruvate as an and 4 and transamination or which Phe into PHA with of into pyridoxamine The transamination an acid to to the of the revealed that CO2, and were in stoichiometric in to PHA a reaction, the of CO2, and PHA formation were and of respectively. of the of the in the shown Fig. the of in the shown in Fig. was under conditions in which into the mixture from the was and formation was and of PAAS of the In the of the formation of PHA was for at 4 h The of PHA in 4 h in the under conditions the in the the PAAS was performed at a in a the of PHA was of the under suggesting that the of can a in the of by under the of decarboxylation by 3,4-dihydroxyphenylalanine is about of that in the of M. Biochem. J. PubMed Scopus Google Scholar). The of and its to of and under conditions the of transamination in the PAAS and was by the of and as amino group The of PHA formation was not by the of the formation of PHA from Phe by PAAS the of the and amino the of was by experiments with of to which as the of PHA, that of the in the of by at the of the resulting in PHA However, PHA was by and at a suggesting that decarboxylation and A PHA labeling pattern was in petunia petals were and floral scent was collected over a Moreover, the formation of from also out and that phenylpyruvate an a deamination the of an which of PHA via or that or is the respectively. However, no was during the PAAS Moreover, PAAS was with 2-phenylethylamine as a no PHA, or was suggesting that PAAS 2-phenylethylamine in the amine or that 2-phenylethylamine is not a in deamination of 2-phenylethylamine to PHA, and amine amine were the PAAS by and a or no PAAS respectively. contain amine or amine as a group 2003; PubMed Scopus Google Scholar, J. H. van A. D. Biochem. 33: PubMed Scopus Google Scholar). The of or at as well as the of acid or such as sodium and sodium not the of PHA Moreover, of PAAS for h at 4 in no its the of it by also not the of These that the in in the of of and in the which from of were to PAAS protein, no or formation was of PAAS with E. coli or the of PAAS to a results that PAAS is a enzyme that catalyzes a and an at the The of PAAS to decarboxylation and oxidation is not other decarboxylases coli PubMed Scopus Google Scholar), M. S. B. 1998; PubMed Scopus Google Scholar, M. M. J. Biol. Chem. 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Full Text PDF PubMed Google Scholar). the of with is also to a are with of the of as an Similar to the of with the of PAAS is shown to in Fig. without In to to C-1 of the as in Fig. the peroxide hydrogen peroxide and the other A in which is known to in have been well such is D. Sci. U. S. A. PubMed Scopus Google Scholar). enzyme catalyzes the of and The and a and D. Sci. U. S. A. PubMed Scopus Google Scholar). of a enzyme that catalyzes a is enzyme catalyzes the of with and of with F. E. Sci. U. S. A. 2004; PubMed Scopus Google Scholar). The of in two is not D. Sci. U. S. A. PubMed Scopus Google Scholar), but the intermediates by a over which the D. Sci. U. S. A. PubMed Scopus Google Scholar, L. J. Chem. 2001; PubMed Scopus Google Scholar). A enzyme that in a is enzyme catalyzes the in the biosynthesis of in and is a enzyme that also a but does not or G. 2004; PubMed Scopus Google Scholar). In PAAS is the enzyme to described in its catalyzes the stoichiometric oxidative decarboxylation of an acid PAAS and a two is under decarboxylation is an oxidative in the by PAAS and a in the by PAAS catalyzes a oxidative decarboxylation of acid catalyzes a decarboxylation of acid PAAS Phe as an oxidative but not as an oxidative but not utilization by PAAS under conditions is with the formation of utilization by is not with the of et al. D. M. N. Sci. U. S. A. Scopus Google Scholar) identified in tomato of the that catalyzes the decarboxylation of Phe to which is from the enzyme and can to phenylacetaldehyde the of a amine of the that in in the by We for with for with and for the of an with