Deamination of phenylalanine

Until recently (43), only E-monolignols were considered to be involved in the process of lignification. This concept of exclusivity presumably arose from the following observations stereospecific deamination of phenylalanine, by phenylalanine ammonia lyase (PAL), affords E-cinnamic acid... 

Oxidative deamination of phenylalanine by phenylalanine ammonia lyase (PAL) and 4-hydroxylation affords p-coumaric acid, whose derivatives are the fundamental building blocks of lignin, as well as the... 

T. intermedins IFO14230 (ATCC 33205) was first identihed as a source of PDH by Ohshima et al." The enzyme was purified and characterized" and then cloned and expressed in E. coli by the same workers. The enzyme was reported to be moderately specihc for deamination of phenylalanine and to carry out the amination of some keto acids at a much lower rate than amination of phenylpyruvate." In our screening, the enzyme was the most effective amino acid dehydrogenase identified for the reductive amination of the keto acid acetal. 

In the phenylpropanoid pathway, the first biosynthetic step leading to SA is a deamination of phenylalanine to CA which is catalyzed by phenylalanine ammonia lyase (PAL). This enzyme is induced by a range of biotic and abiotic stress conditions and is a key regulator in the phenylpropanoid pathway, which yields a variety of phenolics among others involved in structural and defense-related functions [42]. In recent years, PAL and its corresponding genes have been subject of numerous studies in various plant species [43 7]. 

Scheme 12.22. A representation of the deamination of phenylalanine (Phe,F) to (F)-cinnamic acid and the conversion of the latter into more highly oxidized derivatives. The caffeic acid and ferulic acid serve as introductory compounds to phenylpropanoids. EC numbers and some graphic materials provided in this scheme have been taken from appropriate links in a URL starting with http //www.chem.qmul.ac.uk/iubmb/enzyme/.

Biosynthesis of Plant Phenoiics. Phenolic compounds in plant foods are secondary metabolites which are derived from phenylalanine, and in some plants from tyrosine via enzymatic deamination assisted by ammonia lyase (Figure 1). Phenylpropanoids, the first products of deamination of phenylalanine and/or tyrosine consist of a phenyl ring (C ) and a 3 carbon side chain (C,). These Q-C, compounds may subsequently undergo hydroxylation in the phenyl ring and possibly subsequent methylation. This would lead to the formation of a large number of products which include cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid and sinapic acid (5). 

Blaschke-Cobet and co-workers (212) have shown that the non-anthranilate portion of the 2-arylquinolin-4(lH)-one of graveoline of Ruta graveolens is derived from the decarboxylation and deamination of phenylalanine. Feeding experiments with labeled isotopes in R. graveolens indicated that hydroxylation of the aromatic ring precedes cyclization to the quinolin-4(lH)-one system. A (3-keto ester and a 3-carboxyquinolin-4(lH)-one are probable intermediates in the biosynthesis of graveoline (Do) (Scheme 11). 

The envisaged transition from an aquatic to a terrestrial environment was accompanied by, or was dependent upon, evolution of new biochemical pathways, particularly those leading to the phenylpropanoids. The first conunitted step in the phenylpropanoid pathway involves deamination of phenylalanine, Phe 1 (or, in a few instances, tyrosine, Tyr 2) to afford the corresponding cinnamic 3 or p-coumaric 4 acids, respectively [reviewed in Ref. (S)]. Elaboration of the pathway, shown in Figure 1, thus provided a... 

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. 

As Figure 1 depicts, phenylalanine ammonia-lyase (PAL), which occurs ubiquitously in higher plants and the wood-rotting Basidiomycetes (1-3), seems to play a common central role in the conversion of phenylalanine (by deamination) to a wide variety of secondary metabolites. These include lignins in higher plants (4), veratryl alcohol in the white-rot fungus Phanerochaete chrysosporium (4a), and methyl p-anisate in the brown-rot fungus... 

The general phenylpropanoid pathway begins with the deamination of L-phenylalanine to cinnamic acid catalyzed by phenylalanine ammonia lyase (PAL), Fig. (1), the branch-point enzyme between primary (shikimate pathway) and secondary (phenylpropanoid) metabolism [5-7]. Due to the position of PAL at the entry point of phenylpropanoid metabolism, this enzyme has the potential to play a regulatory role in phenolic-compound production. The importance of this is illustrated by the high degree of regulation both during development as well as in response to environmental stimuli. 

We may therefore take for granted that failure of renal deamination of appreciable amounts of tyrosine, tryptophan, and phenylalanine may produce vascular effects, and that disturbances of similar more complex mechanisms for synthesis or metabolism may cause even greater ones. The evidence, however, that amines are actually present in increased amounts in chronic hypertension must be examined. Methods for their measurement are on the whole unsatisfactory. There is a strong suggestion, however, that amines are in general present in higher concentrations in the blood of hypertensives than of normal subjects (57, 59). Occasionally, however, they are found in large amounts in the latter. 

L-Phenylalanine ammonia lyase (PAL EC 4.3.1.5), an enzyme found in a variety of plants, catalyzes both the deamination of L-phenylalanine to (L )-3-phenyl-2-butenoic acid and the reverse reaction33-36. 

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). 

Contrary to the case of free a-amino acids, deamination-substitution of esters of a-amino acids generally proceeds with racemization with excess inversion about the a-carbon atom. However, reaction of the ethyl ester of phenylalanine and its derivatives with sodium nitrite in trifluoroacetic acid affords substitution products with retention of configuration and migration products with inversion of configuration. This result may be explained by assuming initial formation of the phenonium intermediate (2 Scheme 6). ... 

Histidine ammonia-lyase is the first enzyme in the degradation pathway of L-histidine and catalyzes the nonoxidative deamination of histidine (12) to form w r-urocanic acid (13) plus ammonia (Equation (3)). Histidine ammonia-lyase is present in several bacteria and in animals. The mechanism for the reaction that is catalyzed by histidine ammonia-lyase is presumed to be similar to that described above for phenylalanine ammonia-lyase (see Scheme 3). 

The established migration of the aryl group in the deamination reaction of phenylalanine ester has been ingeniously utilized in a synthesis of some tropane alkaloids. Thus, treatment of the 3a-tropanyl ester (19) of ( )-phenyl-alanine with nitrous acid affords a separable mixture of atropine (20), the 3a-tropanyl ester (21) of ( + )-3-hydroxy-3-phenylpropionate, apo-atropine (22), and 3a-tropanyl rrans-cinnamate (23). Although not obtained in a pure state the cis-isomer of (23), and littorine (24), were also shown to be present in the product mixture. ... 

Fig. 6.4.1 Deamination of D-phenylalanine by immobilized DAAO. ( ) phenylalanine (I phenylpynivic acid (a) phenylacetic acid...

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