Prephenate dehydratase

Figure 1. Schematic outline of various products and associated enzymes from the shikimate and phenolic pathways in plants (and some microorganisms). Enzymes (1) 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase (2) 5-dehydroquinate synthase (3) shikimate dehydrogenase (4) shikimate kinase (5) 5-enol-pyruvylshikimate-3-phosphate synthase (6) chorismate synthase (7) chorismate mutase (8) prephenate dehydrogenase (9) tyrosine aminotransferase (10) prephenate dehydratase (11) phenylalanine aminotransferase (12) anthranilate synthase (13) tryptophan synthase (14) phenylalanine ammonia-lyase (15) tyrosine ammonia-lyase and (16) polyphenol oxidase. (From ACS Symposium Series No. 181, 1982) (62).

AGIRE computer program for, 249, 79-81, 225-226 comparison to analysis based on rates, 249, 61-63 complex reactions, 249, 75-78 experimental design, 249, 84-85 inhibitor effects, 249, 71-75 potato acid phosphatase product inhibition, 249, 73-74 preliminary fitting, 249, 82-84 prephenate dehydratase product inhibition, 249, 72-73 product inhibition effects, 249, 72-73 prostate acid phosphatase phenyl phosphate hydrolysis, 249, 70 reactions with two substrates, 249, 75-77 reversible reactions, 249, 77-78 with simple Michaelian enzyme, 249, 63-71 [fitting equations, 249, 63] with slow-binding inhibitors, 249, 88 with unstable enzymes, for kinetic characterization, 249, 85-89. 

PHENYLALANINE DEHYDROGENASE PREPHENATE DEHYDRATASE PHENYLPYRUVATE SYNTHASE PHI (< or4))... 

CROWN ETHER MARCUS THEORY PREPHENATE DEHYDRATASE PREPHENATE DEHYDROGENASE Pressure,... 

Chemical properties appropriate to a compound found at a branch point of metabolism are displayed by chorismic acid. Simply warming the compound in acidic aqueous solution yields a mixture of prephen-ate and para-hydroxybenzoate (corresponding to reactions h and l of Fig. 25-1). Note that the latter reaction is a simple elimination of the enolate anion of pyruvate. As indicated in Fig. 25-1, these reactions correspond to only two of several metabolic reactions of the chorismate ion. In E. coli the formation of phe-nylpyruvate (steps h and i, Fig. 25-1) is catalyzed by a single protein molecule with two distinctly different enzymatic activities chorismate mutase and prephenate dehydratase.34-36 However, in some organisms the enzymes are separate.37 Both of the reactions catalyzed by these enzymes also occur spontaneously upon warming chorismic acid in acidic solution. The chorismate mutase reaction, which is unique in its mechanism,373 is discussed in Box 9-E. Stereochemical studies indicate that the formation of phenylpyruvate in Fig. 25-1, step z, occurs via a... 

FIGURE 3.3 L-Phenylalanine-mediated feedback inhibition of wild-type Escherichia coli K12 prephenate dehydratase (JN302) and four feedback inhibition-resistant enzyme variants (JN305-JN308). Activity is expressed as a percentage of normal wild-type enzyme activity. 

Over the past decade, several strains of yeast [43, 44] and E. coli [45, 46] have been engineered that lack chorismate mutase. A typical bacterial selection system is depicted schematically in Fig. 3.5. It is based on E. coli strain KA12 [45], which has deletions of the chromosomal genes for both bifunctional chorismate mutases (chorismate mutase-prephenate dehydrogenase and chorismate mutase-prephenate dehydratase). Monofunctional versions of prephenate dehydratase [47] and prephenate dehydrogenase [48] from other organisms are supplied by the plasmid pKIMP-UAUC, leaving the cells deficient only in chorismate mutase activity [45]. 

Fig. 3.5. An engineered E. coli selection system lacking endogenous chorismate mutase activity [45]. The genes encoding the bifunctional enzymes chorismate mutase-prephenate dehydrogenase and chorismate mutase-prephenate dehydratase were deleted, and monofunctional versions of the dehydrogenase and dehydratase were supplied on plasmid pKIMP-UAUC. Poten-...

Deregulation of Chorismate Mutase and Prephenate Dehydratase Activity... 

Figure 2 Feedback inhibition profiles of prephenate dehydratase variants in E-coU K12.

The Previous Enigma of Arogenate and/or Prephenate Dehydratases in Plants ... 

Bacterial Prephenate Dehydratases and Plant Arogenate Dehydratases ... 

Fig. 8. From chorismate to phenylalanine and tyrosine. (PDHY = prephenate dehydratase EC 4.2.1.51 PDH = prephenate dehydrogenase EC 1.3.1.13 TAT = tyrosine aminotransferase EC 2.6.1.5 PREPAT = prephanate aminotransferase PTDH = pretyrosine dehydrogenase.)...

Figure 4. Enzymes of Rhizobium (a) and Lemna (b) proposed as sites of glyphosate inhibition of aromatic amino acid synthesis. Abbreviations CM, chorismate mutase PDH, prephenate dehydrogenase and PD, prephenate dehydratase.

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