Prephenate dehydrogenase

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

Gene symbols are according to those of E. coli. (173). Abbreviations Horn, Homoserine Ant, Anthranilic acid PR, Phosphoribosyl ppc, Phosphoenolpyruvate carboxylase PRDH, prephenate dehydrogenase. 

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).

This enzyme [EC 1.3.1.43], also referred to as arogenate dehydrogenase and pretyrosine dehydrogenase, catalyzes the reaction of arogenate with NAD+ to produce tyrosine, NADH, and carbon dioxide. Both prephenate and D-prephenyllactate can act as alternative substrates. 

This enzyme [EC 1.3.1.12], also known as hydroxyphe-nylpyruvate synthase or prephenate dehydrogenase, catalyzes the NAD+-dependent oxidation of prephenate to form 4-hydroxyphenylpyruvate, CO2 and NADH. The following is a recent review on the molecular and physical properties of this synthase. 

Prephenate dehydrogenase [EC 1.3.1.12] catalyzes the reaction of prephenate with NAD+ to produce 4-hydro-xyphenylpyruvate, carbon dioxide, and NADH. This enzyme in enteric bacteria also possesses chorismate mutase activity and converts chorismate into prephenate. Prephenate dehydrogenase (NADP+) [EC 1.3.1.13] catalyzes the reaction of prephenate with NADP+ to produce 4-hydroxyphenylpyruvate, carbon dioxide, and NADPH. 

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

Enzyme Assays. Procedures for the HPLC assay of prephenate aminotransferase (32), the spectrophotometric assay of shikimate dehydrogenase... 

In E. coli and many other bacteria a second bifunctional enzyme, chorismate mutase-prephenate dehydrogenase causes the isomerization of chorismate and the oxidative decarboxylation of prephenate to p-hydroxyphenylpyruvate (steps h and /c, Fig. 25-l).39 The latter can be converted by transamination to tyrosine.40-42... 

The bacterial enzyme chorismate mutase-prephenate dehydrogenase is peculiar because it is a single protein unit with two catalytic activities. It catalyzes the sequential reactions of mutation of chorismate to prephenate and then the reaction that leads to the formation of phenylalanine and tyrosine, through oxidation of prephenate. The first of these reactions is interesting because it is one of the few strictly single-substrate enzymatic reactions it entails... 

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-...

Prephenic acid has also been shown to be converted (by a partly purified enzyme preparation) to p-hydroxyphenylpyruvic acid. Diphosphop3rridine nucleotide was required for this reaction, suggesting oxidation of C4, followed by decarboxylation. This -prephenic dehydrogenase was missing in... 

The aroF gene lies in an operon with tyrA, which encodes the bi functional protein chorismate mutase/prephenate dehydrogenase. Both genes arc regulated by the TyrR repressor protein complexed with tyrosine. The aroF gene product accounts for 80% of the total DAHP synthase activity in wild-type F. coli cells. 

Enzymatic studies with chorismate mutase prephenate dehydrogenase from Escherichia coli show that the chorismate prephenate analog 7 is not a substrate for chorismate mutase65. Both 7 and 8 are moderately competitive inhibitors for chorismate mutase. Ester derivatives 4 and 5, as well as 6, readily undergo Claisen rearrangements in organic solvents. 

The Enigma of Prephenate and/or /Vogenate Dehydrogenases in Plants The Enigma of Prephenate and/or Phenylpyruvate/p-Hydroxyphenylpyruvate Aminotransferases in Plants Regulation of /Vomatic /Voino Acid Biosynthesis... 

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