Biosynthesis of Shikimic Acid

Heptuloses were believed to be concerned in the biosynthesis of shikimic acid, an intermediate in the biosynthesis of aromatic com-poundsd However, despite the excellent utilization of sedoheptulose... 

C7H,0,oP, Mr 286.13. DAHP is an intermediate in the biosynthesis of shikimic acid and is formed by enzymatic addition of phosphoenolpyruvic acid to o- erythrose 4-phosphate by means of phospho-2-dehy-dro-3-deoxyheptanoate aldolase (DAHP synthase, EC 4.1.2.15). 

CjHjObP, Mr 168.04, exists in physiological solution as the dianion, it is a central metabolic product of glycolysis, gluconeogenesis, and the biosynthesis of shikimic acid. Free PEP is not stable stable derivatives include the crystalline metal salts, barium silver PEP trihydrate, monosodium PEP hydrate, calcium bis-PEP dihydrate. 

Several tracer studies of the biosynthesis of (—)-shikimic acid in higher plants have been made and these all accord with the view that, as in micro-organisms, the seven-carbon skeleton of the alicyclic acid is derived by an initial condensation of D-erythrose-4-phosphate (7) and phosphoenolpyruvate (8), Figure 1.2. Uniform labelling of (—)-shikimic acid was obtained by exposure of living plant tissues to carbon dioxide for extended periods " . Short-term exposure gave (—)-shikimic acid with 25 per cent of the isotope in the carboxyl group . This was rationalist on the basis... 

Nature utilizes the shikimate pathway for the biosynthesis of amino acids with aryl side chains. These nonprotein amino acids are often synthesized through intermediates found in the shikimate pathway. In many cases, L-a-amino acids are functionalized at different sites to yield nonprotein amino acids. These modifications include oxidation, hydroxylation, halogenation, methylation, and thiolation. In addition to these modifications, nature also utilizes modified biosynthetic pathways to produce compounds that are structurally more complex. When analyzing the structures of these nonprotein amino acids, one can generally identify the structural similarities to one of the L-a-amino acids with aromatic side chains. 

The shikimate pathway was identified through the study of ultraviolet light-induced mutants of E. coli, Aerobacter aerogenes, and Neurospora. In 1950, using the penicillin enrichment technique (Chapter 26), Davis obtained a series of mutants of E. coli that would not grow without the addition of aromatic substances.4 5 A number of the mutants required five compounds tyrosine, phenylalanine, tryptophan, p-aminobenzoic acid, and a trace of p-hydroxybenzoic acid. It was a surprise to find that the requirements for all five compounds could be met by the addition of shikimic acid, an aliphatic compound that was then regarded as a rare plant acid. Thus, shikimate was implicated as an intermediate in the biosynthesis of the three aromatic amino acids and of other essential aromatic substances.6 7... 

In recent years, agribusiness firms have developed pf empirically several compounds that inhibit essential steps in the biosynthesis of amino acids found in plants but missing in animals. One of these compounds, glyphosate, is a highly specific inhibitor of 5-enol pyruvyl-shikimate-3-phosphate synthase (an enzyme needed for aromatic amino acid biosynthesis). Glyphosate is the active ingredient in the widely used herbicide Roundup. 

The biosynthesis of gallic acid (3.47) has been under investigation for more than 50 years. Different biosynthetic routes have been proposed, as depicted in Figure 3-6 (/) direct biosynthesis from an intermediate of the shikimate pathway, (2) biosynthesis via phenylalanine (3.27), cinnamic acid (3.29), />coumaric acid (3.30), caffeic acid (3.32), and 3,4, 5-trihydroxycinnamic acid (3.44), or (3) biosynthesis via caffeic acid (3.32) and protocatechuic acid (3.45). The possibility that different pathways co-existed in different species or even within one species was also considered. 

Campbell, M.M. et al. The Biosynthesis and Synthesis of Shikimic Acid, Chorismic Acid, and Related Compounds. 1993 [45]... 

When such strains as E. coli 83-24, which are blocked after shikimic acid, were grown on minimal medium plus aromatic supplement, they accumulated 400-800 mg. of shikimic acid per liter, together with variable amounts of shikimate 5-phosphate. Since no mutants that are blocked between shikimic acid and its phosphorylated form were found, it was considered that the phosphate ester is not on the main path of biosynthesis. As will be pointed out later, enzymic studies showed that shikimate 5-phosphate is actually an intermediate between shikimate and the aromatic compounds. It would appear, therefore, that the block in such strains as E. coli 83-24 is probably immediately after shikimate 5-phosphate. With filtrates from this organism, methods were developed for the isolation of pure shikimate and for its stepwise degradation. ... 

Phenazines.—Shikimic acid (134) is clearly implicated as a precursor for microbial phenazines, e.g. iodinin (135), and it can act as the sole source of the carbon skeleton. Essential proof that two molecules of shikimic acid are involved in phenazine biosynthesis was provided when it was shown that on incorporation of DL-[1,6- C2, 2- H]shikimic acid [as (134)] into iodinin (135) in Brevibacterium iodinum, some (7.5%) of the molecules of (135) produced were dideuteriated. [The shikimic acid was incorporated with the usual high efficiency (similar values for and H) and the deuterium label was confined to the expected positions (see below).]... 

Further support for the conclusion that two molecules of shikimic acid are involved in phenazine biosynthesis comes from the incorporation of >-[1,6,7,- CaJshikimic acid [as (134)] into phenazine-1-carboxylic acid (138) in Pseudomonas aureofaciens with close to a fifth of the activity present in the carboxy-group, as required if two molecules of shikimic acid are involved [however, the same result would have been obtained if only one molecule of shikimic add was implicated provided that a symmetrical intermediate of type (139) was also involved in the elaboration of (138)]. 

Two molecules of shikimic acid (87) are used for the construction of the phenazine ring system diversion from the shikimate pathway to phenazine biosynthesis seems to occur at... 

The above results do not allow one to decide whether one or two molecules of shikimic acid are involved in the biosynthesis of the phenazine nucleus but there is other evidencethat the number of molecules involved is two. If this is accepted there are two ways in which the shikimic acid units can be arranged, (181) and (182) (181) is preferred, for such an arrangement of C-, units is to be seen in phenazine-1,6-dicarboxylic acid (183) and in the griseoluteins, e.g. griseolutein A (184). ... 

The biosynthesis of shikimate, the direct precursor for chorismate, has been reviewed elsewhere 138-141). The shikimate pathway leading to chorismate is located in the plastids. For the two branches from chorismate leading to the aromatic amino acids, it has been postulated that both occur in a plastidial and a cytosolic form 142). The plastidial form is responsible for the aromatic amino acids for primary metabolism, and the cytosolic one for the biosynthesis of the aromatic amino acids used as precursors in secondary metabolism (for a review, see refs. 141,143). 

C7H8O5, Mr 172.14, needles, mp. 146-147 °C, [a]p -57° (C2H5OH). D. is isolated as the direct biosynthetic precursor of shikimic acid from culture filtrates of Escherichia coli and is widely distributed in nature. The biosynthesis proceeds through cleavage of water from 3-dehydroquinic acid. 

Glyphosate (4.56) which hinders steps in the biosynthesis of chorismic acid is a successful herbicide devising other agents by inhibiting shikimic, prephenic, and chorismic acids is open for further exploration. 

Biosynthesis of Dehydroquinic Acid Shikimic Acid and Chorismic Acid (Fig. 143)... 

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. 

Figure 3. The biosynthesis of chorismic acid and protocatechuic acid from 3-dehydroshikimic acid (3... dehydrase 4... shikimate-dehydrogenase).

A rather unique branch of the shikimate pathway operates in the biosynthesis of naphthoquinones related to vitamin K (menaquinone) (Fig. 30). Seven of the ten carbon atoms of the naphthoquinone ring system are derived from the seven carbon atoms of shikimic acid. The remaining three carbons are provided by the three center carbon atoms of a-ketoglutaric acid in a reaction leading to the unique intermediate o-succinylbenzoic acid. Cyclization of the latter produces the intermediate 1,4-dihydroxynaphthoic acid, the substrate for an isoprenylation reaction which occurs with simultaneous loss of COa Methylation of the 3 position then completes the reaction sequence. Studies by Meganathan and Bentley had indicated that chorismic acid is the substrate for the thiamine pyrophosphate-... 

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... 

Fig. 63.3 Pathway of the shikimic acid in the biosynthesis of phenolic acids...

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