Phenylalanine microbial

Many microbial sources of enzymes suitable for converting them into L-phenylalanine... 

Although 2-phenylethanol can be synthesised by normal microbial metabolism, the final concentrations in the culture broth of selected microorganisms generally remain very low [110, 111] therefore, de novo synthesis cannot be a strategy for an economically viable bioprocesses. Nevertheless, the microbial production of 2-phenylethanol can be greatly increased by adding the amino acid L-phenylalanine to the medium. The commonly accepted route from l-phenylalanine to 2-phenylethanol in yeasts is by transamination of the amino acid to phenylpyruvate, decarboxylation to phenylacetaldehyde and reduction to the alcohol, first described by Ehrlich [112] and named after him (Scheme 23.8). 

Fig. 23.5 Aqueous-organic two-liquid-phase system for microbial production of flavour compounds. Here the formation of 2-phenylethanol from L-phenylalanine is exemplarily shown [120]. The organic solvent used for in situ extraction has to be carefully selected on the basis of multiple criteria, such as biocompatibility, non-flammability and legislative regulations. For a more detailed description of flavour production in two-phase systems, see Chap. 24 by Larroche et al.

Microbial Catabolism of Phenylalanine, Tyrosine, and Other Aromatic Compounds... 

A large number of a, 3-didehydro-a-amino acids have been identified as constituents of relatively low molecular weight cyclic compounds from microbial sources. However, the presence of a,p-didehydroalanine in bacterial as well as in mammalian histidine ammonia lyase and in phenylalanine ammonia lyase shows that the occurrence of a,p-didehydro-a-amino acids is not limited to small molecules alone 8 These residues are incorporated in natural sequences by posttranslation modification. a,p-Didehydro-a-amino acids have also been postulated to be precursors in the biosynthesis of several heterocyclic metabolites including penicillin and cephalosporin 9 Other well-known compounds containing ,( -di-dehydro-a-amino acids are nisin 10,11 (a food preservative112 ), subtilin (a broad spectrum antibiotic) 13 and some of the metabolites isolated from Streptomyces strains such as gri-seoviridin 14 ... 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

RL Hanson, JM Howell, TL LaPorte, MJ Donovan, DL Cazzulino, V Zannella, MA Montana, VB Nanduri, SR Schwarz, RF Eiring, SC Durand, JM Wasylyk, WL Parker, LJ Szarka, RN Patel. Synthesis of allysine ethylene acetal using phenylalanine dehydrogenase from Thermoactinomyces intermedins. Enzyme Microbial Technol 26 348-358, 1999. 

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). 

Indolmydn.—Previous evidence on the biosynthesis of indolmycin (88) in Strepto-myces griseus cultures accords with the pathway shown in Scheme 4. The first two steps in the pathway have been carried out using cell-free extracts of 5. griseus - and recent work has led to the isolation of two enzymes which can effect these transformations. The first, tryptophan transaminase, catalysed the pyridoxal phosphate-dependent transamination of L-tryptophan, but not D-trptophan, and in common with some other microbial transaminases, a-ketoglutarate was an efficient amino-group acceptor. L-Phenylalanine, tyrosine, and 3-methyltryptophan (this compound inhibited enzyme function) also underwent transamination. 

The shikimate pathway of aromatic acid biosynthesis is the source of building blocks for a very wide number of natural products from microbial and plant kingdoms. Remarkably, it appears that this pathway is the unique source for the de novo synthesis of phenylalanine, tyrosine, and tryptophan. Although many shikimate-derived... 

The resolution of N-acetyl-D,L-amino acids to prepare non-natural l- and D-amino acids was the beginning of applied biocatalysis, and aminobutyric and di-amino-butyric acids as well as beta-D,L-phenylalanines can be resolved. A series of microbial acylases from Streptomyces, Alcaligenes, Comamonas and Pseudomonas species were produced for these applications. Immobilized acylase on Eupergit C or the use of membrane reactors allow the facile production of such chiral amino acids. 

Often, cells of a single microbial strain can synthesize more than one member of a chemical family. The final yields of the various members can be shifted by appropriate precursor pressure. The absence or presence of certain growth factors may accomplish this. In the absence of either exogenous phenylalanine or tryptophan, the ratio of tyrocidines A B C synthesized by Bacillus brevis is 1 3 7. If either L- or D-phenylalanine is provided, the main component formed is tyrocidine A. If L- or D-tryptophan is furnished, component D predominates when both phenylalanine and tryptophan are supplied, each of the four components is synthesized. I ... 

S )-Enantiomcrs of fluorophcnylalanincs and 4-(trifluoromethyl)phenylalanine were successfully prepared from the corresponding 2-oxo acids by the transfer of an amino group from (S)-aspartic acid catalyzed by a specific transaminase of microbial origin20. The biomimetic reduction of other imines with NAD coenzymes has also been described21 28. 

Cytochalasins.—The cytochalasins are a group of microbial metabolites of biological interest. Biosynthetic experiments with radioactively labelled materials have indicated that cytochalasin B (186) is formed from phenylalanine (the carboxy-group being retained), nine acetate units, and two Ci units which derive from methionine label from malonate was also incorporated. From these results, which are summarized in (188), it was suggested that cytochalasin B is derived from a Cjg (or Ci6, if C-19 and C-19a represent a separate acetate unit) polyketide chain, initiated by acetate and propagated by malonate. 

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