Biosynthesis chorismate synthase

A feedback inhibition has been detected in B. subtilis, using the ferrisiderophore reductase. This enzyme reduces iron from the ferrisiderophore. The rate at which the ferrisiderophore reductase reduces iron from ferrisiderophores may signal the aromatic pathway about the demand for chorismic acid for 2,3-DHBA synthesis [128,129]. The reductase may have a regulatory effect on chorismate synthase activity. Chorismate synthase may have oxidizable sulfhydryl groups that, when oxidized, may slow the synthesis of chorismic acid [128-130]. There seemed to be no repression or inhibitory effect of 2,3-DHBA or SA on its own biosynthesis [78,121]. Also the endproduct mycobactin (sole endproduct) does not inhibit SA biosynthesis [78]. 

Chorismate Synthase. - Chorismate synthase catalyses the conversion of 5-enolpyruvylshikimate-3-phosphate to chorismate. It is the seventh and last enzyme of the shikimate pathway. Chorismate constitutes a major building block for the biosynthesis of an array of aromatic compounds, including the amino acids phenylalanine, tryptophan and tyrosine. Although this reaction does not involve a change in redox states, the enzyme requires reduced FMN for activity, and binds oxidized flavin only very weakly which results in its isolation as the flavin-free apo-enzyme. Macheroux and co-workers have used spectrophotometry, fluorimetry and EPR and ENDOR to investigate binding of the oxidized, reduced and radical forms of FMN to chorismate synthase in the presence of (6R)-6-fluoro-5-enolpyruvylshikimate-3-phosphate(a substrate ana-... 

Anthranilic acid (or o-amino-benzoic acid) is an aromatic acid with the formula C H NO, which consists of a substituted benzene ring with two adjacent, or "ortho- functional groups, a carboxylic acid, and an amine (Fig. 14.1). Anthranilic acid is biosynthesized from shikimic acid (for shikimic acid biosynthesis, see Chapter 10) following the chorismic acid-mediated pathway [1]. Based on its biosynthetic mechanism, shikimate is transformed to shikimate 3-phosphate with the consumption of one molecule of ATP, catalyzed by shikimate kinase. 5-Enolpyruvylshikimate-3-phosphate (EPSP) synthase is then catalyze the addition of phosphoenolpyruvate to 3-phospho-shikimate followed by the elimination of phosphate, which leads to EPSP. EPSP is further transformed into chorismate by chorismate synthase. Chorismate reacts with glutamine to afford the final product anthranilate and glutamate pyruvate catalyzed by anthranilate synthase (Fig. 14.1). 

This enzyme [EC 4.1.3.27] catalyzes the reaction of chorismate with glutamine to generate anthranilate, pyruvate, and glutamate. In certain species, this enzyme is part of a multifunctional protein together with one or more other components of the system for the biosynthesis of tryptophan (Le., indole-3-glycerol-phosphate synthase, anthranilate phosphoribosyltransferase, tryptophan synthase, and phosphoribosylanthranilate isomerase). The anthranilate synthase that is present in these complexes has been reported to be able to utilize either glutamine or ammonia as the nitrogen source. However, it has also been reported that when anthranilate synthase is separated from this complex, only ammonia can serve as a substrate. 

The biosynthesis of tryptophan from the branchpoint compound, chorismate in E. coli The first step involves the conversion of chorismate to the aromatic compound anthranilate. The anthranilate is transferred to a ribose phosphate chain. The product is cyclized to indoleglycerol phosphate by the removal of water and loss of the ring carboxyl by indoleglycerol phosphate synthase. Finally, in a... 

The first specific step in tryptophan biosynthesis is the glutamine-dependent conversion of chorismate to the simple aromatic compound anthranilate. Like most other glutamine-dependent reactions, the reaction can also occur with ammonia as the source of the amino group. However, high concentrations of ammonia are required. Thus far, almost all the anthranilate synthases examined have the glutamine amidotransferase activity (component II) and the choris-mate-to-anthranilate activity (component I) on separate proteins. 

Figure 3-5. Biosynthesis of salicylic acid. The enzymes involved in this pathway are (a) chorismate mutase (E.C. 5.4.99.5), (b) prephenate aminotransferase (E.C. 2.6.1.78 and E.C. 2.6.1.79), (c) arogenate dehydratase (E.C. 4.2.1.91), (d) phenylalanine ammonia lyase (E.C. 4.3.1.5), (e) presumed P-oxidation by a yet to be identified enzyme, (f) benzoic acid 2-hydroxylase, (g) isochorismate synthase (E. C. 5.4.4.2), and (h) a putative plant pyruvate lyase.

By use of synthetic medium the formation of 3,4-trans-CH D was maintained for a 36-h cultivation period, resulting in accumulation of up to 790 mg L 1 3,4-trans-CHD 1 [11]. With this strain, however, it is necessary to separate the growth and production phases, because the substances for which E. coli strain BN117 is known to be auxotrophic, i.e. tryptophan, tyrosine, phenylalanine, proline, arginine, histidine, and p-aminobenzoate, also partially inhibit entry to the chorismate biosynthesis pathway (feedback inhibition of DAHP-synthase). 

Isochorismate synthase, that might be involved in the biosynthesis of 2,3-DHBA, has recently been purified from Catharanthus roseus cell-suspension cultures and subsequently its gene was cloned (L. van Tegelen, P. Moreno, A. Croes, G. Wullems and R. Verpoorte, submitted for publication). Two isoforms of the enzyme were purified and characterized. Both have an apparent molecular mass of 65 kD. The Km values for chorismic acid are 558 pM and 319 p.M for isoform I and II respectively. The enzymes are not inhibited by aromatic amino acids and require Mg for enzyme activity. The isolated cDNA encodes a protein of 64 kD with a A-terminal chloroplast targeting signal. The deduced amino acid sequence shares homology with bacterial isochorismate synthases, and also with anthranilate synthases, another chorismate utilizing enzyme. 

Enzymes and genes involved in the 2,3-DHBA biosynthesis When in 1968 the intermediates of 2,3-DHBA biosynthesis were identified [85], it became clear that isochorismate synthase (isochorismate hydroxy mutase) is the enzyme that converts chorismic acid to isochorismic acid. 2,3-Dihydro-2,3-DHBA synthase (or isochorismatase) converts isochorismic acid to 2,3-dihydro-2,3-DHBA and finally... 

Candicidin production by Streptomyces griseus was inhibited by inorganic phosphate, which suppressed the biosynthesis of p-aminobenzoate, the starter unit for the synthesis of this 38-membered heptaene macrolide antibiotic [95]. P-aminobenzoic acid synthase (PABA synthase) catalyses the conversion of chorismic acid to PABA, which is a precursor to candicidin. 

L-Tryptophan is formed through a biosynthetic pathway consisting of five enzymatically controlled steps (152). In plants, tryptophan is required for protein synthesis and also provides precursors for secondary metabolites, such as indole alkaloids. The formation of anthranilate and the following four steps in the tryptophan biosynthesis are invariant in all organisms studied to date (153) (Fig. 9). Anthranilate synthase (AS, EC 4.1.3.27) catalyzes the conversion of chorismate to anthranilate, the first step in this pathway. 

Plants synthesize all 20 common amino acids de novo. Glyphosate, a weed killer sold under the trade name Roundup, is an analog of phosphoenolpyruvate that specifically inhibits 3-enolpyruvylshikimate 5-phosphate synthase, a key enzyme of the pathway for chorismate biosynthesis. This compound is a very effective plant herbicide, but has virtually no effect on mammals. Why ... 

CioHiqOs, Mr 226.19, important intermediate in the biosynthesis of salicylic acid, vitamin K, and side-rophores. The biosynthesis proceeds through rearrangement of chorismic acid by means of isochoris-mate synthase (EC 5.4.99.6) see also Lit.. ... 

Biosynthesis Like other aromatic amino acids, e.g., Phe and Tyr, Trp is formed on the shikimic acid pathway. There is a branching point at chorismic acid one branch leads to Phe and Tyr, the other to Trp choris-mic acid - anthranilic acid (anthranilic acid synthase, EC 4.1.3.27)- A-(5 -0-phosphoribosyl)-anthranilic acid (anthranilic acid phosphoribosyl transferase, EC 2.4.2.18)- 1 -o-carboxyphenylamino-1 -deoxyribu-lose 5-phosphate [A-(5 -phosphoribosyl)anthranilic acid isomerase]- indole-3-glycerol phosphate (in-dole-3-glycerol phosphate synthase, EC 4.1.1.48) - indole (tryptophan synthase, EC 4.2.1,20)+serine - Trp. Many biologically active indole compounds are derived from Trp, e. g., 5-hydroxytryptophan, 5-hydroxy-tryptamine ( serotonin), and melatonin as well as many indole alkaloids. 

The biosynthesis of many secondary metabolites is inhibited by processes resembling feedback inhibition. The end-product repression of arylamine synthase, an enzyme catalyzing the amination of chorismic acid to an aromatic amine which serves as an intermediate in chloramphenicol biosynthesis, was described (29). 

Figure 5.41 Early steps of the proposed indole acetic acid biosynthesis pathways for Ara-bidopsis. CHO, chorismate ANA, anthranilate PANA, 5-phosphoribosylanthranilate CADP, l-(o-carboxyphenylamino)-l-deoxyribulose-5-phosphate IGP, indole-3-glycerol phosphate TRP, tryptophan. Enzymes ASA, anthranilate synthetase, suhunit a ASB, anthranilate synthetase, suhunit P PAT, phosphorihosylanthranUate transferase PAI, phosphoiibosylanthrani-late isomerase IGS, indole-3-glycerol-phosphate synthase TSA, tryptophan synthase, subunit a and TSB, tryptophan synthase, suhunit p.

Trp is synthesized in bacteria and plants via shiki-mate and chorismate (Fig. 2) (see Aromatic biosynthesis, L-Hyptophan synthase). 

Fig. 144. Biosynthesis of naphthoquinone and anthraquinone derivatives from chorismic acid 1 2-Succinylbenzoate synthase 2 2-succinylbenzoate Co A ligase, naphthoate synthase 3 l,4-dihydroxy-2-naphtho-ate polyprenyltransferase...

Fig. 9. Sequential pattern of allosteric control over biosynthesis of aromatic amino acids in the plastid compartment. In the presence of excess aromatic amino acids, L-tyrosine (TYR) inhibits arogenate dehydrogenase, L-phenylalanine (PHE) inhibits arogenate dehydratase and L-tryptophan (TRP) inhibits anthranilate synthase. The three aromatic amino acids exert allosteric inhibition (-) or activation (+) effects upon chorismate mutase-1 as symbolized. However, activation dominates over inhibition. The outcome of these events is to trap L-arogenate (AGN) between the various foci of control in the pathway. As shown symbolically, -arogenate (AGN) then acts to feedback inhibit DAHP synthase-Mn.

L-Tyrosine biosynthesis starts with the condensation of phosphoenolpyruvate (PEP) and erythrose-4-phosphate (E4P), the intermediates of the glycolytic pathway and pentose phosphate pathway, respectively, which is catalyzed by 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS aroE/aroG/aroH). The resultant 3-deoxy-D-arabino-heptulosonate (DAHP) is converted into chorismate through the shikimate pathway with seven reactions. In plants, prephenate (PPA) is converted into L-arogenate by transamination whereas in E. coli, PPA is converted to p-hydroxyphenylpyruvate (HPP) by prephenate dehydrogenase, which is a bifunctional enzyme that behaves as chorismate mutase/prephenate... 

Figure 7. Metabolic pathways that use chorismate as a starting material The SgcD/SgcG-dependentpathway is specific to C-1027 biosynthesis (shaded) and represents the newest pathway originating from chorismate. ADC, 4-amino-4-deoxychorismate ASI, anthranilate synthase component I IC, isochorismate SA, salicylic acid ADIC, 2-amino-2-deoxyisochorismate OPA, 2-enolpyruvylanthranilate.

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