Ammonia lyase, tyrosine

Figure 1. Schematic outline of various products and associated enzymes from the shikimate and phenolic pathways in plants (and some microorganisms). Enzymes (1) 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase (2) 5-dehydroquinate synthase (3) shikimate dehydrogenase (4) shikimate kinase (5) 5-enol-pyruvylshikimate-3-phosphate synthase (6) chorismate synthase (7) chorismate mutase (8) prephenate dehydrogenase (9) tyrosine aminotransferase (10) prephenate dehydratase (11) phenylalanine aminotransferase (12) anthranilate synthase (13) tryptophan synthase (14) phenylalanine ammonia-lyase (15) tyrosine ammonia-lyase and (16) polyphenol oxidase. (From ACS Symposium Series No. 181, 1982) (62).

The key reaction that links primary and secondary metabolism is provided by the enzyme phenylalanine ammonia lyase (PAL) which catalyzes the deamination of l-phenylalanine to form iran.v-cinnamic acid with the release of NH3 (see Fig. 3.3). Tyrosine is similarly deaminated by tyrosine ammonia lyase (TAL) to produce 4-hydroxycinnamic acid and NH3. The released NH3 is probably fixed by the glutamine synthetase reaction. These deaminations initiate the main phenylpropanoid pathway. 

Watts KT, Mijts BN, Lee PC, Manning AJ, Schmidt-Dannert C (2006) Discovery of a substrate selectivity switch in tyrosine ammonia-lyase, a member of the aromatic amino acid lyase family. Chem Biol 13(12) 1317-1326... 

The chemical and physical evidence for the presence of lignin in the material deposited at wound margins is supported by biochemical studies on the enzymes involved in phenylpropanoid metabolism. Thus, the extractable activities of phenylalanine ammonia-lyase, tyrosine ammonia-lyase, cinnamate-4-hydroxylase, caffeic acid O-methyltransferase,... 

Enzymatic preparations for PAL from monocotyledonous species (monocots) can show a similar activity against tyrosine (tyrosine ammonia lyase, TAL), and TAL enzymatic preparations also show PAL activity. That a single enzyme may account for the observed cooccurring TAL and PAL activities was confirmed by Rosier et al., who showed the recombinant Zea mays (maize) PAL converted tyrosine to 4-coumarate directly, thus removing the requirement for the usual 4-hydroxylation step in phenylpropanoid biosynthesis. 

Rosier, J. et al., Maize phenylalanine ammonia-lyase has tyrosine ammonia-lyase activity. Plant Physiol, 113, 175, 1997. 

PAL activity in soybean seedlings was increased by several herbicides such as DPX-4189, glyphosate and acifluorfen [112,113]. Also, the activities of PAL and tyrosine ammonia lyase (TAL) in both maize and soybean seedlings were also increased by alachlor [110] and metolachlor [111]. 

Figure 3-4. The general phenylpropanoid pathway. The enzymes involved in this pathway are (a) phenylalanine ammonia lyase (PAL E.C. 4.3.1.5), (b) cinnamic acid 4-hydroxylase (C4H E.C. 1.14.13.11), and (J) 4-coumaric acid CoA ligase (4CL E.C. 6.2.1.12). (a) depicts tyrosine ammonia lyase activity in PAL of graminaceous species. The grey structures in the box represent an older version of the phenylpropanoid pathway in which the ring substitution reactions were thought to occur at the level of the hydroxycinnamic acids and/or hydroxycinnamoyl esters. The enzymes involved in these conversions are (c) coumarate 3-hydroxylase (C3H E.C. 1.14.14.1), (d) caffeate O-methyltransferase (COMT EC 2.1.1.68), (e) ferulate 5-hydroxylase (F5H EC 1.14.13), and (g) caffeoyl-CoA O-methyltransferase (CCoA-OMT EC 2.1.1.104). These enzymes are discussed in more detail in Section 10.

The tomato plant contains a number of enzymes that we have already discussed and that may be important mediators of resistance to insects (e.g., polyphenol oxidases, peroxidases, lipoxygenases, ureases, chitinases, phenylalanine and tyrosine ammonia lyases, en-dopolygalacturonases). We discuss here the potential interaction of these enzymes. 

Figure 3. Diagram of Multicomponent Defenses in the Tomato Plant. PHE - phenylalanine TYR - tyrosine POD - peroxidase PPO - polyphenol oxidase PAL - phenylalanine ammonia lyase TAL — tyrosine ammonia lyase.

T Higuchi, Y Ito, I Kawamura. /J-Hydroxyphenylpropane components of grass lignin and the role of tyrosine ammonia-lyase in its formation. Phytochemistry 6 875-881, 1967. 

Oxidation of Phenolic Compounds. Phenolic compounds are widespread throughout the plant kingdom and are prevalent in fruits where they are important contributors to color and flavor (46). Phenolic compounds, particularly flavonoids and derivatives of chlorogenic acid, play a crucial role in the development of a number of postharvest disorders through their oxidation to brown compounds that discolor many fruits and vegetables and substantially reduce their quality. A number of enzymes catalyze the biosynthesis or oxidation of phenolic compounds, among them phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL), cinnamic acid-4-hydroxylase (CA4H), polyphenol oxidase (PPO), and catechol oxidase (CAO). The chemistry... 

Biochemical Mechanisms of Phenylalanine and Tyrosine Ammonia Lyases Comparison to Histidine Ammonia Lyases... 

Figure 4 Current view of the phenylpropanoid pathway to the monolignols 19-23. 4CL, 4-hydroxycinnamate coenzyme Aligases pC3H , p-coumarate 3-hydroxylase C4H, cinnamate 4-hydroxylase CAD, cinnamyl alcohol dehydrogenases CCOMT, hydroxycinnamoyl CoA O-methyltransferases CCR, cinnamoyl-CoA oxidoreductases COMT, caffeic acid O-methyltransferases F5H , ferulate 5-hydroxylase HCT, hydroxycinnamoyl-CoA shikimate hydroxycinnamoyltransferase HOT, hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase PAL, phenylalanine ammonia lyase TAL, tyrosine ammonia lyase.

Figure 11 Reactions catalyzed by phenylalanine and tyrosine ammonia lyases.

We have presented evidence (124) that phenylalanine and tyrosine ammonia lyases, two enzymes induced during wounding, have the potential to limit the insects intake of free phenylalanine... 

The first step of flavonone biosynthesis begins with the deamination of the amino acid phenylalanine or tyrosine by a phenylalanine ammonia-lyase (PAL) or a tyrosine ammonia-lyase (TAL), which affords cinnamic acid and p-coumaric acid, respectively (Figure 6.36). The formed cinnamic acid is first hydroxylated to p-coumaric acid by a membrane-bound P450 monooxygenase, cinnamate 4-hydroxylase (C4H), and then activated to p-coumaroyl-CoA by a 4-coumarate-CoA ligase (4CL). 4CL catalyzes also the conversion of caffeic acid, feruhc acid, and cinnamic acid to caffeoyl-CoA, feruloyl-CoA, and cinnamoyl-CoA, respectively. 

Some grasses (Poaceae or Gramineae) have the corresponding enzyme, L-tyrosine ammonia lyase (TAL), capable of converting L-tyrosine (5) into p-coumarate (2), but this enzyme is not widely distributed. TAL also acts in a highly stereospecific manner. The reaction also proceeds with removal of the pro-3S-hydrogen from the -methylene atom of L-tyrosine. It is not completely resolved that this enzyme is distinct from PAL (Hanson and Havir, 1981). 

Fig. 27.4. Phenylalanine ammonia lyase and tyrosine ammonia lyase monoamine and diamine oxidases (Geissman and Grout, 1969).

In plants and microorganisms cinnamic acid is formed from L-phenylalanine by phenylalanine ammonia-lyase (PAL). This enzyme catalyzes the antiperiplanar elimination of the pro 3S-hydrogen atom and of the NHg-group to yield trans-cinnamic acid (Fig. 294). Most PAL preparations deaminate also L-tyrosine, but to a smaller extend. In some organisms a special tyrosine ammonia-lyase exists. 

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