Biosynthetic pathways, common aromatic

All amino acids are derived from intermediates in glycolysis, the citric acid cycle, or the pentose phosphate pathway (Fig. 22-9). Nitrogen enters these pathways by way of glutamate and glutamine. Some pathways are simple, others are not. Ten of the amino acids are just one or several steps removed from the common metabolite from which they are derived. The biosynthetic pathways for others, such as the aromatic amino acids, are more complex. 

The biosynthetic pathway from SA into L-Phe [69, 70] is shown in Fig. 8.15. The synthesis of chorismate (CHA), the common intermediate in the biosynthesis of the aromatic amino acids, requires an extra equivalent of PEP, which limits the yield of L-Phe from glucose to 0.30 mol mol-1 if PEP is not conserved [91]. The further transformation of CHA into phenylpyruvic acid (PPY) suffers from inhibition by L-Phe and is also subject to transcriptional control [69, 92]. The final step is a reductive amination of PPY into L-Phe with consumption of l-G1u. 

L-isoleucine, and L-tryptophan was observed, suggesting that 123 likely shares a common biosynthetic pathway with the paraherquamides as shown in Fig. (28). Prenylation of the cyc/o-L-tryptophan-L-13-methylproline and intramolecular [4+2] cyclization (via 126) would provide the putative bicyclo[2,2,2] core (127). Williams and coworkers have already demonstrated that 127 serves as a biosynthetic precursor to paraherquamide A (146) shown in Fig. (33). Oxidation of 127 leads to the catechol derivative (128). Oxidative cleavage of four carbon atoms from the oxygenated aromatic ring in 128 could furnish the spirosuccinimide ring of 123. 

Deoxy-D-arahmo-heptulosonate 7-phosphate (DAHP) synthase is the first enzyme of the common aromatic biosynthetic pathway in bacteria and plants (212). Three such isozymes have been identified in E. coli, which are sensitive to phenylalanine, tyrosine, and tryptophan, respectively. The tyrosine-sensitive DAHP synthase has been found to contain approximately one iron per mole of enzyme and to exhibit an absorption maximum at... 

Considerable progress has also been made in elucidating the biosynthetic pathway leading to the podophyllotoxin series (scheme 2) [38,39]. Dewick et al. have shown that demethylyatein (15a) and yatein (15b) are precursors of demethylpodophyllotoxin (18a) and podophyllotoxin (18b) respectively. Furthermore, 4 -demethyl-deoxypodophyllotoxin (16a) and deoxypodophyllotoxin (16b) undergo aromatic hydroxylation to yield a-peltatin (17a) and p-peltatin (17b) respectively. They have also shown that (-)-matairesinol (13) is efficiently incorporated into 4 -demethylpodophyllotoxin (18a), podophyllotoxin (18b), a-peltatin (17a) and p-peltatin (17b). These facts have been interpreted as indicating that matairesinol is a common precursor of both the 3,4,5-trimethoxyphenyl and 4-hydroxy-3,5-dimethoxyphenyl series. 

It is challenging to give an accurate, succinct definition of what a lipid is. Most commonly, lipids are thought of as fatty acids and the related triglycerides, but even this does not include the mono- and di-substituted glycerol compounds. In general terms, lipids can be considered to be fatty acids, their derivatives and any other compounds that may have a similar behaviour, functionality or biosynthetic pathway. They are often hydrophobic, soluble in hydrocarbon or aromatic solvents and insoluble in water. 

Extensive studies support the hypothesis that these phenazine precursors are derived from the shikimic acid pathway, as outlined in Scheme 1, with chorismic acid (51) as the most probable branch point intermediate. Shikimic acid (50) is converted to chorismic acid (51) in known transformations that are part of the common aromatic amino acid biosynthetic pathway. The transformation from chorismic acid (51) to the phenazine precursors has been discussed and investigated through intensive biochemical studies so far, no intermediates have been identified and little is known about the genetic origin and details of the phenazine biosynthesis. ... 

The tryptophan biosynthetic pathway in microorganisms is one of the branches from a common pathway for the biosynthesis of the aromatic substances. Some regulation of tryptophan synthesis occurs at the level of the common aromatic pathway as well as at the level of the synthesis of glutamine [1,2], a tryptophan precursor. This chapter will be... 

The early history of the analyses which disclosed the major features of the tryptophan biosynthetic pathway was reviewed by Yanofsky [7] and by Umbarger and Davis [8], and the more recent history by Gibson and Pittard [3]. The pathway is shown in Fig. 1. Chorismate, a substrate of the first reaction in the tryptophan pathway, is the branch-point intermediate at the end of the common aromatic pathway [9,10]... 

The aromatic biosynthetic pathways do not exist in isolation. Some interactions among the branches of the common aromatic pathway have been mentioned in this chapter. Substrates which are common to several different pathways can serve to interconnect the functioning of the pathways, although they may appear to be quite independent. Jensen has coined the term metabolic interlock to describe regulatory interactions among different metabolic pathways [146a,243,244]. A number of reports have appeared of interactions between the histidine and tryptophan pathways in B. subtilis involving effects on the rates of enzyme synthesis [245,246] as well as enzyme activity [244], Evidence for an interaction between the histidine and tryptophan pathways of N. crassa has also been reported [247],... 

Tryptophan, phenylalanine, and tyrosine are biosynthesized through the common aromatic amino acid biosynthetic pathway (Figure 12.4). Tryptophan finds application in feed and pharmaceutical industries. Tryptophan in animal diets increases quality of pork, maximizes feed utilization, and reduces nitrogen excretion. The Chinese producer Ajinomoto holds 73% of the global production with a volume of 100 million dollars and Evonik 18%. ... 

Bacteria, fungi, and plants share a common pathway for the biosynthesis of aromatic amino acids with shikimic acid as a common intermediate and therefore named after it—the shikimate pathway. Availability of shikimic acid has proven to provide growth requirements to tryptophan, tyrosine, and phenylalanine triple auxotrophic bacterial strains. Chorismate is also the last common precursor in the aromatic amino acid biosynthetic pathway, but the pathway is not named after it, as it failed to provide growth requirements to the triple auxotrophs. The aromatic biosynthetic pathway starts with two molecules of phosphoenol pyruvate and one molecule of erythrose 4-phosphate and reach the common precursor, chorismate through shikimate. From chorismate, the pathway branches to form phenylalanine and tyrosine in one and tryptophan in another. Tryptophan biosynthesis proceeds from chorismate in five steps in all organisms. Phenylalanine and tyrosine can be produced by either or both of the two biosynthetic routes. So phenylalanine can be synthesized from arogenate or phenylpyruvate whereas tyrosine can be synthesized from arogenate or 4-hydroxy phenylpyruvate. 

The precursors of flavonoid biosynthesis include shikimic acid, phenylalanine, cinnamic acid, and p-coumaric acid. Shikimic acid acts as an intermediate in the biosynthesis of aromatic acid. The basic pathways to the core isoflavonoid skeletons have been established both enzymatically and genetically [16]. The synthesis of isoflavones can be broadly divided into three main synthetic pathways the formylation of deoxybenzoins, the oxidative rearrangement of chalcones and flavanones, and the arylation of a preformed chromanone ring. In leguminous plants, the major isoflavonoids are produced via two branches of the isoflavonoid biosynthetic pathway, and the different branches share a majority of common reactions [1]. Unlike the common flavonoid compotmds, which have a 2-phenyl-benzopyrone core structure, isoflavones, such as daidzein and genistein, are 3-phenyl-benzopyrone compounds. Biochemically, the synthesis of isoflavones is an offshoot of the flavonoids biosynthesis pathway. Several attempts have aimed to increase... 

The ansamycin antibiotics represent a new class of natural products, combining an aromatic nucleus with a branching aliphatic side chain, and considerable interest has centered on their formation in nature. Their common structural features suggest immediately a similar biosynthetic pathway. Moreover, the streptovaricins, rifamycins, tolypo-micin B and halomicin B all have the same number of carbon atoms in the ansa ring (C17), while geldanamycin and the maytansinoids also have the same number of carbon atoms (C15). Thus far, biosynthetic... 

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