Aromatics biosynthesis

Transgenic soybean plants expressing the CTP-CP4 EPSPS display commercial levels of Roundup tolerance. These results vaUdate the importance of substrate kinetics of EPSPS in order to maintain adequate rates of aromatic biosynthesis. Furthermore, the fact that glyphosate tolerance can be obtained by expression of a glyphosate-tolerant EPSPS illustrates that the herbicidal mode of action of glyphosate is related solely to inhibition of the EPSPS reaction. 

Ratledge C (1964) Relationship between the Products of Aromatic Biosynthesis in Mycobacterium smegmatis and Aerobacter aerogenes. Nature 203 428... 

Figure 25-1 Aromatic biosynthesis by the shikimate pathway. The symbols for several of the genes coding for the required enzymes are indicated. Their locations on the E. coli chromosome map are shown in Fig. 26-4. The aminoshikimate pathway which is initiated through 4-aminoDAHP leads to rifamycin and many other nitrogen-containing products.

Exchange of Function in the Aromatic Biosynthesis Pathways Trp and His Pathways... 

Recently Frost and Rosenberg (56) demonstrated that strains of K-12 blocked in aromatic biosynthesis and also tonB" could fabricate enterobactin from precursors such as 2,3-dihydroxybenzoic acid. The siderophore synthesized endogenously from 2,3-dihydroxybenzoic acid was pictured as carrying iron from the periplasmic space across the cytoplasmic membrane. Evidently ferric enterobactin could not traverse the outer membrane in these strains. 

Enolpyruvate phosphate and n-erythrose 4-phosphate are independent intermediates in metabolic pathways of n-glucose that are not directly concerned with aromatic biosynthesis. Their simultaneous requirement for shikimate formation therefore indicates the first specific, or branch-point,... 

Further support for 3-deoxy-D-arofefno-heptulosonic acid 7-phosphate as an intermediate in aromatic biosynthesis was given by the isolation of a phosphorylated keto acid from filtrates of a mutant of E. cali, blocked before 5-dehydroquinate. This compound was shown to be identical with synthetic 3-deoxy-D-ara wno-heptulosonic acid 7-phosphate by its chromatographic behavior, chemical properties, and conversion to 5-dehydroquinate by a purified enzyme-preparation. ... 

This phosphorylation was not inhibited by any of the end products of aromatic biosynthesis. ... 

Some microorganisms may resemble the higher organisms in being able to convert phenylalanine directly to tyrosine thus it can occur in Vibrio (167) and Pseudomonas (605) and has been claimed for E. coli (48 but cf. 807). However in Lactobacillus arabinosus tyrosine is formed by a route not involving phenylalanine (20), as is apparently also the case in Aero-bacter aerogenes (605). The direct conversion of phenylalanine to tyrosine is claimed by advocates of the straight-chain pathway of aromatic biosynthesis described later. 

The information at present available is thus sufficient to exclude certain possible routes for aromatic biosynthesis, but is not yet sufficient to reveal the actual mechanism or mechanisms used, or to define parts of the pathway. But it seems probable that the techniques available are adequate to deal with the problem and that perhaps in a short time the present obscurities will be made clear. 

Further information and pertinent speculations on aromatic biosynthesis can be found in reviews by Ehrensvard (212) and Davis (191). 

In discussing the use of mutants of microorganisms in the study of aromatic biosynthesis it was pointed out that valuable information could thus be obtained. An organism with a metabolic block rendering it unable to convert a substance X into its metabolite Y is likely either to excrete X, or to metabolize X by an alternative pathway if such is available, or to excrete metabolites of X formed by the action of relatively unspecific detoxicating systems. Accumulation or excretion of abnormal substances may therefore indicate an enzymic deficiency of this type. In the latter part of... 

S ATP + shikimate <3, 17, 19> (<3> SK2 is the isoenzyme that normally functions in aromatic biosynthesis in the cell, SKI functions only when high intracellular levels of shikimate occurs [3] <19> energy charge plays a role in regulating shikimate kinase, thereby controlling the shikimate pathway [10] <17> the enzyme catalyzes the committed step in the seven-step biosynthesis of chorismate [18]) (Reversibility <3, 17, 19> [3, 10, 18]) [3, 10, 18]... 

Catalyzed conversion of D-glucose into c/s, c/s-muconic acid (27) required creation of a biosynthetic pathway not known to exist naturally (Figure 5). This pathway relied on DHS dehydratase (Figure 5, enzyme A) (44,45) to couple aromatic biosynthesis to... 

Hydroxyl groups are also inserted into ring B at the aromatic level to generate 4 -hydroxy-, 3 -4 -dihydroxy-, and 3, 4, 5 -trihydroxy-substituted derivatives (ortho positions). These products are commonly complexed with sugar residues held in glycosidic linkage, which renders them more soluble. Only matters related to biosynthesis of the acetate-derived portion will be dealt with in this section aspects of aromatic biosynthesis and hydroxyla-tion of ring B are covered in Volume 7 of this treatise. 

The pentose family includes histidine and the 3 aromatic A. a. (see Aromatic biosynthesis), phenylalanine, tyrosine and tryptophan. 

Aromatic biosynthesis, aromatizatioa biosynthesis of compounds containing the benzene ring system. The most important mechanisms are 1. the shi-kimate/chorismate pathway, in which the aromatic amino acids, L-phenylalanine, L-tyrosine and L-trypto-phan, 4-hydroxybenzoic acid (precursor of ubiquinone), 4-aminobenzoie acid (precursor of folic acid) and the phenylpropanes, including components of lignin, cinnamic acid derivatives and flavonoids are synthesized and 2. the polyketide pathway (see Polyke-tides) in which acetate molecules are condensed and aromatic compounds (e.g. 6-methylsalicylic acid) are synthesized via poly-fl-keto acids. Biosynthesis of flavonoids (e.g. anthocyanidins) can occur by either pathway. 

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