L-tyrosine ammonia lyase

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). 

In higher plants the polymer, lignin, and various aromatic secondary metabolites, notably many alkaloids (Chapter 6) and flavonoids (Section 5.4) are formed from the aromatic amino acids, L-phenylalanine (5.77) and/or L-tyrosine (5.75). [For some alkaloids as well as some microbial metabolites, tryptophan (5.7 ) is the source of their particular aromatic rings.] There are for these metabolites common pathways leading from phenylalanine, and in some plants tyrosine, to phenylpropanoid (Cg-Cg) intermediates. The first step from phenylalanine involves the enzyme L-phenylalanine ammonia lyase (known, perhaps affectionately, as PAL), an enzyme widely distributed, and well-characterized. Elimination of ammonia occurs to give cinnamic acid 5.23). It involves loss of the (3-/ ro-5)-proton of L-phenylalanine (5.77), and thus occurs in the aw z-sense [L-tyrosine ammonia lyase functions to remove also the (3-/ ro-5)-proton in tyrosine] [12, 13]. 

L-Tyrosine ammonia lyase acts in a similarly highly stereospecific manner upon its typical substrate as does L-phenylalanine ammonia lyase, and Battersby and Hanson and their collaborators shoVved that the reaction proceeded with removal of the proS hydrogen (44, Ha) from the jS-methylene carbon atom of L-tyrosine to generate trans-p-coumarate (9). 

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. 

Catabolism of histidine in most organisms proceeds via an initial elimination of NH3 to form urocanic acid (Eq. 14-44). The absence of the enzyme L-histidine ammonia-lyase (histidase) causes the genetic disease histidinemia 284/285 A similar reaction is catalyzed by the important plant enzyme L-phenylalanine ammonia-lyase. It eliminates -NH3+ along with the pro-S hydrogen in the (3 position of phenylalanine to form frans-cinnamate (Eq. 14-45). Tyrosine is converted to p-coumarate by the same enzyme. Cinnamate and coumarate are formed in higher plants and are converted into a vast array of derivatives (Box 21-E,... 

L-Dopa Addition of ammonia with L-tyrosine phenol lyase from Erwinia herbicolad 250 t/y Ajinomoto [9]... 

Biosynthesis. The primary precursors of L. are con-iferyl, sinapyl and p-coumaiyl alcohoi, which are derived from 4-hydroxycinnamic acid. L. from conifers (i. e. from softwood) is derived chiefly from conifeiyl alcohol with variable but small proportions of sinapyl and p-coumaryl alcohol. L. from dicotyledonous an-giosperms (i.e. from hardwood), particularly deciduous trees, is formed chiefly from sinapyl (-44%) and coniferyl (-48 %) alcohol, with about 8 % p-cou-maryl alcohol. L. in grasses is formed from p-coumar-yl (-30%), coniferyl (-50%) and sinapyl (-20%) alcohol. These primary L. precursors are formed from the aromatic amino acids L-phenylalanine and L-tyro-sine by a series of reactions shown (Rg.). The first reaction is catalysed by L-Phenylalanine ammonia-lyase (EC 4.3.1.5) (see) this enzyme is induced by light in a process involving phytochrome, and it is of general importance in the synthesis of plant phenolic compounds from phenylalanine and tyrosine. 

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. 

The aromatic amino acid L-phenylalanine (primary metabolite) is directed into the phe-nylpropanoid pathway leading to hydroxy-cinnamic acids, lignin and flavonoids by the activity of L-phenylalanine ammonia-lyase (PAL), which brings about its nonoxidative deamination yielding ammonia and tvans-cinnamic acid (Fig. 1). PAL is one of the most studied plant enzymes, and its crystal structure has recently been solved [2]. PAL is related to the histidine and tyrosine ammonia-lyases of amino acid catabolism. A class of bifunctional PALs found in monocotyle-donous plants and yeast can also deaminate tyrosine [3]. A single His residue is responsible for this switch in substrate preference [3, 4]. All three enzymes share a unique MIO (4-methylidene-imidazole-5-one) prosthetic group at the active site. This is formed auto-catalytically from the tripeptide Ala-Ser-Gly by cyclization and dehydration during a late... 

Phenol is formed from L-tyrosine and its derivatives in some bacterial cultures not through a stepwise degradation of the molecule but through primary fission of the side chain. The L-tyrosine inducible enzyme L-tyrosine phenol lyase has been prepared in crystalline form from cell extracts of Escherichia intermedia A-21 and a molecular weight of 170000 was estimated . The enzyme catalyses the stoichiometric conversion of L-tyrosine (5) to phenol (20), pyruvate (21) and ammonia in the presence of added pyridoxal phosphate as a cofactor. Brot, Smit and Weissbach have described... 

Tyrosine phenol lyase (p-tyrosinase) has been shown to catalyze the efficient synthesis of the L-amino acids L-tyrosine and L-dopa from pyruvate, ammonia and phenol, or catechol, respectively (87-89). 

Decarboxylases of phenylalanine, tyrosine, and lysine and ammonia lyases of histidine, glutamine, and asparagine are also highly selective. Guilbault et al. (1988) described a potentiometric enzyme sensor for the determination of the artificial sweetener aspartame (L-aspartyl-L-phen-ylalanine methylester) based on L-aspartase (EC 4.3.1.1). The ammonia liberated in the enzyme reaction created a slope of 30 mV/decade for the enzyme-covered ammonia sensitive electrode. The specificity of the sensor was excellent however, the measuring time of 40 min per sample appears not to be acceptable. The measuring time has been decreased to about 20 min by coimmobilizing carboxypeptidase A with L-aspartase (Fatibello-Filho et al., 1988). 

A further industrially important lyase for the production of L-amino acids is the tyrosine phenol lyase [39]. This biocatalyst is used by Ajinomoto in the production of the pharmaceutically important L-3,4-dihydroxyphenylalanine (L-dopa), 32, which is applied in the treatment of Parkinson s disease. The reaction concept is based on a one-pot three-component synthesis starting from catechol, 30, pyruvic acid, 31, and ammonia in the presence of suspended whole cells (strain Erwinia herbicola) containing the tyrosine phenol lyase biocatalyst (Fig. 16). A key feature of this process is the high volumetric productivity of 110 g/L of the desired L-dopa product. Notably, this reaction runs with an annual capacity of 250 tons. 

Tyrosine phenol-lyase (TPL) is a pyridoxal 5 -phosphate-dependent multifunctional enzyme and catalyzes degradation of tyrosine into phenol, pyruvate, and ammonia. This reaction is reversible and the reverse reaction is available to produce l-DOPA using pyrocatechol instead of phenol. 

However, of industrial importance is the manufacturing of (L)-3,4-dihy-droxyphenylalanine ((L)-DOPA), an agent against Parkinson s disease, using a tyrosine phenol-lyase. Ajinomoto employs a whole-cell preparation from Er-winia herbicola to obtain the target compound in a three-component reaction, starting from catechol, pyruvic acid and ammonia. The annual capacity amounts to around 250 tonnes. [64]... 

Japanese workers have described a novel microbiological synthesis of L-tyrosine and L-dopa from sodium pyruvate, ammonia and phenol or catechol respectively, using cells of Erwinia herbicola. The reaction is catalysed by tyrosine phenol lyase and is the reverse of the normal a)3-elimination reaction catalysed by this enzyme. The L-tyrosine or L-dopa synthesised by this enzymatic method precipitates from the reaction media during incubation. The maximum amount of L-tyrosine synthesised by this method was 60.5 g per litre and of L-dopa 58.5 g per litre. The process is a variation on the analogous procedure reported by the same school which used d L-serine in place of sodium pyruvate. 

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