Chorismic acid conversion

Phenazines — The phenazines are biosynthesized by the shikimic acid pathway, through the intermediate chorismic acid. The process was studied using different strains of Pseudomonas species, the major producers of phenazines. The best-known phenazine, pyocyanine, seems to be produced from the intermediate phenazine-1-carboxylic acid (PCA). Although intensive biochemical studies were done, not all the details and the intermediates of conversion of chorismic acid to PCA are known. In the first step, PCA is N-methylated by a SAM-dependent methyltransferase. The second step is a hydroxylative decarboxylation catalyzed by a flavoprotein monooxygenase dependent on NADH. PCA is also the precursor of phenazine-1-carboxamide and 1-hydroxyphenazine from Pseudomonas species. - - ... 

Table 1 Kinetic and thermodynamic parameters for the spontaneous, enzyme-catalysed and antibody-catalysed conversion of chorismic acid [23] into prephenic acid [24],...

Chorismic acid (26), thus, represents the first divergence point of pyocyanin from other biosynthetic pathways. The first authentic pyocyanin biosynthetic enzyme is PhzE, which has sequence similarity to anthranilate synthases, which generate anthranilate from chorismate. PhzE is thought to catalyze the conversion of chorismic acid (26) to amine 165. Compound 165 is in turn a substrate for PhzD, an isochorismatase that catalyzes the hydrolysis of the vinyl ether to 166 and pyruvate [188, 189],... 

The biosynthesis of menaquinone is outlined in Fig. 44. Isomerization of chorismate to isochorismate followed by condensation with a-ketogluta-rate and aromatization gives o-succinylbenzoic acid. Conversion of 238 to the CoA thio ester, followed by cyclization, prenylation and methylation completes the biosynthesis. The biosynthesis of the prenyl side chain follows the alternative terpene biosynthetic pathway described for ubiquinone. 

The first intermediate in the biosynthesis of 2,3-DHBA in K. pneumoniae is isochorismic acid. The conversion of chorismic acid to isochorismic acid requires Mg ... 

Experiments on the rate of 2,3-DHBA formation from chorismic acid and the observation that chorismic acid, in the absence of NAD was converted to a compound which could serve as a substrate for 2,3-DHBA formation, indicated that at least two steps were concerned in the conversion of chorismic acid to 2,3-DHBA [84,86]. The first intermediate is isochorismic acid, which is converted to the second intermediate... 

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. 

The studies of the origin of GHB in A. bisporus demonstrated the involvement of the shikimate-chorismate pathway (Scheme 102). Labeling experiments showed an efficient incorporation of H- and C-labeled shikimic acid 439,440) and C-labeled chorismic acid 441) into the 4-hydroxyaniline moiety of GHB. It was also demonstrated that in the biochemical shikimate-4-hydroxyaniline conversion in the mushroom, amination occurred at the 4 position of one of the carboxylic acid intermediates [initially assumed to be shikimic acid 439)]. Additionally, the p-aminobenzoic acid, which proved to be 441) the precursor of 4-hydroxyaniline, underwent a decarboxylative hydroxylation catalyzed by a FAD-dependent monooxygenase 4-aminobenzoate hydroxylase in the presence of NAD(P)H and O2. This enzyme from A. bisporus was recently purified to homogeneity by Tsuji et al. 442). 

The shikimic acid (or shikimate) pathway can be divided into three parts condensation of erythrose-4-phosphate and phosphoenolpyruvate and the subsequent cyclization and production of shikimic acid (Fig. 7.1), alteration of shiki-mate-3-phosphate to chorismic acid (Fig. 7.1), and the conversion of chorismate into other products (Fig. 7.2). The shikimic acid pathway might more appropriately be called the chorismic acid pathway, as that compound is the key intermediate and branching point for most plant secondary compounds produced. 

The first step in the formation of tryptophan involves conversion of chorismate (9) to anthranilate (11) (Fig. 7.4). Although the reaction is not well understood, it is catalyzed by the enzyme anthranilate synthase and utilizes L-gluta-mine. By means of specifically labeled chorismic acid, it was determined that the protonation involved in the formation of anthranilic acid had occurred from the re face (Figure 4) (Floss, 1986). Anthranilic acid (11) also serves as an intermediate for the synthesis of a number of secondary compounds and occurs free and as various derivatives in many plants and other organisms (Dewick, 1989). 

Q 5. With respect to the following biogenetic conversion of chorismic acid (I) to 4-hydroxyphenylpyruvic acid (III), the correct statement is ... 

Chorismic acid is the key branch point intermediate in the biosynthesis of aromatic amino acids in microorganisms and plants (Scheme 1.1a) [1]. In the branch that leads to the production of tyrosine and phenylalanine, chorismate mutase (CM, chorismate-pyruvate mutase, EC 5.4.99.5) is a key enzyme that catalyzes the isomerization of chorismate to prephenate (Scheme 1.1b) with a rate enhancement of about lO -lO -fold. This reaction is one of few pericyclic processes in biology and provides a rare opportunity for understanding how Nature promotes such unusual transformations. The biological importance of the conversion from chorismate to prephenate and the synthetic value of the Claisen rearrangement have led to extensive experimental investigations [2-43]. 

End-product inhibition of AS activity by tryptophan appears to be a rather common control mechanism among microorganisms. Nester and Jensen [71] described tryptophan inhibition of B. subtilis AS activity as the first step in sequential feedback control. Excess tryptophan would result in inhibition of the conversion of chorismate to anthrani-late. The consequent accumulation of chorismic acid would then serve as a feedback inhibitor of the DAMPS, the first enzyme in the pathway leading to chorismate synthesis. Bacillus alvei has an anthranilate synthetase which is extremely sensitive to inhibition by tryptophan [98]. In contrast to the mode of AS feedback inhibition in E. coli and S. typhimurium, the B. alvei AS is inhibited by tryptophan noncom-petitively with respect to chorismate and uncompetitively with respect to glutamine. It is the only Bacillus species, among 21 studied, which did not exhibit a sequential feedback control pattern [79]. 

The information obtained from the application of glyphosate to complex systems strongly pointed to one of the following three enzymes as the target of the inhibitor in the shikimate pathway shikimate kinase (EC 2.7.1.71), 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase (EC 2.5.1.19), and chorismate synthase (EC 4.6.1.4). Jointly, these three enzymes convert shikimic acid to chorismic acid in a series of interesting reactions >(Fig. 2). A defined system" had therefore to be found in which the conversion of shikimic acid to chorismic acid could be conveniently studied. 

In agreement with the assumption > that chorismic acid is the branch point, it was postulated that a cell free system catalyzed the conversion of chorismic acid and a-ketoglutaric acid (III) to o-succinylbenzoic acid (II) Later it became evident, however, that the chorismic acid sample employed in these experiments contained trace amounts of iso-chorismic acid (I). Indeed, iso-chorismic acid (I) is converted to -succinylbenzoic acid (II) in the presence of a-ketoglutaric acid (III) in almost 90% yield. ... 

Enzyme systems have been isolated from Escherichia coli and Aerobacter aerogenes which convert chorismic acid to 2,3-dihydroxybenzoic acid. The enzyme from Aerobacter aerogenes requires magnesium and NAD" for activity and is strongly repressed by low concentrations of iron or cobalt . Omission of the pyridine nucleotide from the enzymic reaction mixture allowed the conversion of chorismic acid to an intermediate (44), which itself was converted to 2,3-dihydroxybenzoic acid on the subsequent addition of The intermediate compoimd was isolated and identified as 5,6-dihydrocyclohexa-l,3-diene-1-carboxylic acid (44) for which the trivial name 2,3-dihydro-2,3-dihydroxybenzoic acid was suggested The structure of the intermediate was established... 

Subsequently a further intermediate in the conversion of chorismic acid to 2,3-dihydroxybenzoic acid was isolated and identified using enzyme extracts of Aerobacter aerogenes. The intermediate was identified as 2-hydroxy-3-(r-carboxyvinloxy)-2,3-dihydrobenzoic acid (40) and was given the trivial name isochorismic acid. The compound was converted enzymically to equimolar amounts of... 

Schultz and coworkers (Jackson et a ., 1988) have generated an antibody which exhibits behaviour similar to the enzyme chorismate mutase. The enzyme catalyses the conversion of chorismate [49] to prephenate [50] as part of the shikimate pathway for the biosynthesis of aromatic amino acids in plants and micro-organisms (Haslam, 1974 Dixon and Webb, 1979). It is unusual for an enzyme in that it does not seem to employ acid-base chemistry, nucleophilic or electrophilic catalysis, metal ions, or redox chemistry. Rather, it binds the substrate and forces it into the appropriate conformation for reaction and stabilizes the transition state, without using distinct catalytic groups. 

Aryl side chain containing L-a-amino acids, such as phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), are derived through the shikimate pathway. The enzymatic transformation of phosphoenolpyr-uvate (PEP) and erythro-4-phosphate, through a series of reactions, yields shikimate (Scheme 2). Although shikimate is an important biosynthetic intermediate for a number of secondary metabolites, this chapter only describes the conversion of shikimate to amino acids containing aryl side chains. In the second part of the biosynthesis, shikimate is converted into chorismate by the addition of PEP to the hydroxyl group at the C5 position. Chorismate is then transformed into prephenate by the enzyme chorismate mutase (Scheme 3). 

During the biosynthetic transformation, chorismate is the point of divergence for the biosynthesis of Phe, Tyr, Trp, and other amino acids containing aromatic groups. For example, the biosynthesis of Trp begins with the conversion of chorismate to anthranilate (Scheme 4(a)). A sequence of amination and aromatization reactions produces anthranilate, which is then condensed with phosphoribosylpyrophosphate. The intermediate is carried through a series of reactions to yield Trp (Scheme 4(b)). 

The conversion of chorismate to prephenate, catalyzed by the enzyme choris-mate mutase, is involved in the biosynthesis of the amino acids phenylalanine and tyrosine. Classify this pericyclic reaction and explain whether it is thermally allowed or not. 

The utilization of evolutionary strategies in the laboratory can be illustrated with proteins that catalyze simple metabolic reactions. One of the simplest such reactions is the conversion of chorismate to prephenate (Fig. 3.3), a [3,3]-sigmatropic rearrangement. This transformation is a key step in the shikimate pathway leading to aromatic amino acids in plants and lower organisms [28, 29]. It is accelerated more than a million-fold by enzymes called chorismate mutases [30],... 

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