Enzymes phenylalanine-ammonia lyase

One of the most interesting uses for cinnamic acid in recent years has been as a raw material in the preparation of L-phenylalanine [63-91-2] the key intermediate for the synthetic dipeptide sweetener aspartame (25). Genex has described a biosynthetic route to L-phenylalanine which involves treatment of immobilized ceUs of R rubra containing the enzyme phenylalanine ammonia lyase (PAT,) with ammonium cinnamate [25459-05-6] (26). 

Reaction 1 is governed by the enzyme phenylalanine ammonia lyase. This enzyme normally conducts the breakdown of L-phenylalanine to from-cinnamic add and ammonia. However, die reaction can be reversed leading to the production of L-phenylalanine from frans-dnnamic add by using excess ammonia. 

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. 

Various commercial routes for the production of L-phenyalanine have been developed because of the utilization of this amino acid in the dipeptide sweetener Aspartame. One route that has been actively pursued is the synthesis of L-phenylalanine from trans-cinnamic acid using the enzyme phenylalanine ammonia lyase (105,106). This enzyme catalyzes the reversible, nonoxidative deamination of L-phenylalanine and can be isolated from various plant and microbial sources (107,108). 

As can be seen from Table 8.7 productivity (expressed in g h b is highest for precursor addition. The production of L-phenylalanine from phenylpyruvic add also has the shortest reaction time to obtain hi conversions. The pH commonly used is around 75, quite normal for biological processes. Only the enzyme phenylalanine ammonia lyase shows an optimiim pH of lO.The process temperature varies between 30 and 40°C with an average of 35°C. No extreme temperatures have been reported due to the fact that denaturation occurs at hi temperatures. The optimal concentration for cells frequently used is 10-20 g 1". However, conversion of ACA is done with hi cell mass concentrations in recent studies possibly to compensate for substrate inhibition and thus to maintain hi product concentration. The processes using PPA and ACA need an amino add as amino donor, usually L-aspartic add is used. 

The enzyme phenylalanine ammonia lyase (EC 4.3.l.S) catalyzes elimination of ammonia from phenylalanine 297a to yield ( )-cinnamic acid 309a, X = H, and various research groups (303,305,306,309) have shown that the 3-pro-S hydrogen, Hp, is eliminated in the process by using the synthetic samples of stereospecifically labeled phenylalanine. Elimination of ammonia is therefore... 

Primary and phenolic metabolism are linked by the well-known enzyme phenylalanine ammonia-lyase (PAL) which converts L-phenylalanine into cinnamic acid. This enzyme has been shown to be present in different cellular fractions with other enzymes involved in phenolic metabolism ... 

The enzyme phenylalanine ammonia-lyase (PAL) catalyses non-oxi-dative deamination of L-phenylalanine to form /ra 5-cinnamic acid... 

As an example of a molecule with diastereotopic ligands, consider the amino acid L-phenylalanine. The two protons at C-3 are diastereotopic, since substitution of either of them would generate a molecule with two chiral centers. Because the chiral center already present is 5, the two diastereomers would be the 2S,3R and the 25,35 stereoisomers. As in the case of enantiotopic protons, diastereotopic protons are designated pro-R or pro-S. The enzyme phenylalanine ammonia lyase catalyzes the conversion of phenylalanine to trans-cinnamic acid by a process involving anti elimination of the amino group and the 3-pro-S hydrogen. This stereochemical course has been demonstrated using deuterium-labeled L-phenyl-alanine as shown" ... 

The possible pathway for the biosynthesis of benzoylacetic acid as building block of phenolic side chain is the following (Fig. 11.18). Phenylalanine is converted into trans-Cinnamic acid by the enzyme phenylalanine ammonia-lyase (PAL). Hydroxylation of Cinnamic acid gave 3-hydroxy-3-phenylpropanoic acid which is transformed to benzoylacetic acid by (3-oxidation (chain degradation). 

The first step of phenylpropanoid biosynthesis is conversion of phenylalanine into cinnamic acid by cleavage of ammonium group by the enzyme phenylalanine ammonia-lyase (PAL). Reduction of carboxylic acid from the cinnamic acid leads to cinnamaldehyde, which is then acylated with acetate from acetyl-CoA to form coniferyl alcohol [14]. Reductive cleavage of coniferyl alcohol by eugenol synthase yields eugenol [15]. 

Phenylpropanoid metabolism is initiated via deamination of the amino acids, Phe 1 and (in some instances) Tyr 2 (7), these conversions being catalyzed by the enzymes, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL), respectively. With one apparent exception, Dunaliella (8), this pathway is absent in algae. Nevertheless, the essential absence of lignins (and related phenylpropanoids) in algae strongly implies that only those acquiring the padiway were able to make the transition to a terrestrial environment. 

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