Shikimate 5-phosphate

The mode of action is by inhibiting 5-enolpymvyl-shikimate-3-phosphate synthase. Roundup shuts down the production of the aromatic amino acids phenylalanine, tyrosine, and tryptophane (30). Whereas all these amino acids are essential to the survival of the plant, tryptophane is especially important because it is the progenitor for indole-3-acetic acid, or auxin, which plays an important role in growth and development, and controls cell extension and organogenesis. 

Example 16 the synthesis of (-)-shikimate-3-phosphate by Shin and Wu [44] using dibenzyl-iV,N-diisopropylphosphoroamidite and subsequent oxidation by CPBA (steps a and b) involves the deprotection of the final triester phosphate by trimethylbromosilane (TMBS) which allows simultaneous removal of benzyl 2,2,3,3-tetramethoxybutane and methyl groups (steps c and d). 

This enzyme [EC 4.6.1.4], also known as 5-enolpyruvyl-shikimate-3-phosphate phospholyase, catalyzes the conversion of 5-0-(l-carboxyvinyl)-3-phosphoshikimate to chorismate and orthophosphate, ft should be noted that shikimate is numbered so that the double bond is between Cl and C2. However, some of the early reports on this enzyme numbered shikimate in the reverse direction. 

SHIKIMATE DEHYDROGENASE SHIKIMATE KINASE Shikimate 3-phosphate,... 

Enolpyruvate shikimate-3-phosphate synthase (EPSPS) is the enzyme that catalyzes the condensation of shikimate-3-phosphate with phosphoenolpymvate. The corresponding difluorophosphonate (phosphoenolpymvate analogue) irreversibly inhibits EPSPS. The mechanism of the inhibition by difluorophosphonate is similar to that reported for MurZ inhibition (Figure 7.31). ... 

Aromatic Amino Acid Biosynthesis. The shikimate pathway is the biosynthetic route to the aromatic amino acids tryptophan, tyrosine and phenylalanine as well as a large number of secondary metabolites such as flavonoids, anthocyanins, auxins and alkaloids. One enzyme in this pathway is 5-enolpyruvyl shikimate-3-phosphate synthase (EPSP synthase) (Figure 2.9). 

The reversible reaction of phosphoenolpyruvate (PEP) with shikimate 3-phosphate is a step in the synthesis of the aromatic amino acids (see Fig. 25-1). The chemical mechanism indicated... 

Shikimate 3-phosphate 687s SH2 / phosphopeptide complex 368s Sialic acid 165s, 183, 546 Sialidase 186... 

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. 

Shikimate is further converted to shikimate 3-phosphate (3.22) by shikimate kinase, and subsequently to 5-e o/pyruvylshikimate 3-phosphate (EPSP 3.23) by 5-e o/pyruvylshikimate 3-phosphate synthase. EPSP is then converted to chorismate (3.24) by chorismate synthase. 

Most of the biotechnologically enhanced plant varieties currently on the market express a new protein, which confers the desired phenotype. For example, Roundup Ready varieties express an introduced form of the protein 5-enolpymvyl-shikimate-3-phosphate synthase (EPSPS), which is slightly different to the endogenous EPSPS protein produced by the plant. This slightly different form is... 

Inhibits 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS), an enzyme of the aromatic acid and biosynthesis pathway. This prevents synthesis of essential aromatic amino acids needed for protein biosynthesis... 

The other compound, called Zl, which was much more acid-labile, was hydrolyzed to equimolar amounts of pyruvate and shikimate, and was tentatively assigned the structure of shikimate 3- or 5-enolpyruvate ether. In a more recent study, it was found that the barium salt of Zl does not absorb in the carbonyl region of the infrared absorption spectrum (no ester structure), and that it has a strong band at 8.2iu characteristic of a vinyl ether. It is oxidized very rapidly by periodate, giving rise to an unstable compound with maximum absorption at 235 m i ( = 4000). A similar unstable chromophore, most likely having the structure XVII, was produced by periodate oxidation of shikimate 3-phosphate but not of shikimate 5-phosphate. (3-Methyl-crotonaldehyde shows Xm 235, t = 6700. ) These observations suggest that Zl is shikimate 3-enolpyruvate ether (XVIII). 

It is now well established that the primary metabolic target of glyphosate is an enzyme of the shikimic acid metabolic pathway, enolpyruvyl shikimate-3-phosphate synthase (2.f ). Via this action, glyphosate blocks the synthesis of the end products of this pathway, notably phenylalanine and tryptophan, but also various subsequent products (Figure 1) ( ,i). It has seemed logical to conclude that the herbicidal effect of glyphosate is a direct result of its effect on the shikimic acid pathway. 

Comparable studies have been performed for the formation of m-cyclo-hexyl fatty acids in Alicydobacillus acidocaldarius and the pathways are identical [100]. A recent publication concerning this later pathway has shown that the final remaining stereochemical ambiguity, the stereochemistry of proton loss at C-6 in the initial 1,4-conjugate elimination of shikimate occurs with loss of the pro-6R proton [102]. This mirrors the stereochemistry of normal shikimate metabolism in the formation of chorismate from 5-enolpyruvyl-shikimate 3-phosphate. 

Phenylalanine, tyrosine, and tryptophan are synthesized by a common pathway in E. coli (Figure 24.13). The initial step is the condensation of phosphoenolpyruvate (a glycolytic intermediate) with erythrose 4-phosphate (a pentose phosphate pathway intermediate). The resulting seven-carbon open-chain sugar is oxidized, loses its phosphoryl group, and cyclizes to 3-dehydroquinate. Dehydration then yields 3-dehydroshikimate, which is reduced by N ADPH to shikimate. The phosphorylation of shikimate by ATP gives shikimate 3-phosphate, which condenses with a second molecule of phosphoenolpyruvate. The resulting 5-enolpyruvyl intermediate loses its... 

Jaworski (4) reported that growth inhibition of both plant and microbes by glyphosate could be reversed by aromatic amino acids. Further work of Amrhein and his coworkers revealed that glyphosate inhibits the shikimate pathway enzyme, 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase (5). This enzyme catalyzes the reaction shown in Figure 1. Glyphosate-treated plant and bacterial cultures accumulate shikimate and/or shikimate 3-phosphate (S3P), confirming that inhibition of EPSPS is at least a part of the in vivo mechanism of action of this herbicide (6, 7). 

The binding of shikimate 3-phosphate (S3P) and glyphosate (a potent, commercially important herbicide) to EPSP synthase provides a good example of two-step reaction kinetics with the first step in rapid equilibrium (33). S3P binds to the enzyme in a rapid equilibrium with rates of kon = 6-5 x 10 sec" and koff = 4500 sec (J). Glyphosate binds only to the enzyme-S3P complex and induces a change in protein fluorescence. Thus the kinetics follow a two-step reaction sequence (Scheme VIll),... 

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