5-Dehydroshikimic reductase

Biosynthesis of Tea Flavonoids. The pathways for the de novo biosynthesis of flavonoids in both soft and woody plants (Pigs. 3 and 4) have been generally elucidated and reviewed in detail (32,51). The regulation and control of these pathways in tea and the nature of the enzymes involved in synthesis in tea have not been studied exhaustively. The key enzymes thought to be involved in the biosynthesis of tea flavonoids are 5-dehydroshikimate reductase (52), phenylalanine ammonia lyase (53), and those associated with the shikimate/arogenate pathway (52). At least 13 enzymes catalyze the formation of plant flavonoids (Table 4). 

Dehydroshikimate reductase and phenylalanine ammonia lyase mediate reactions involved in the synthesis of the polyphenols and are therefore key components of tea leaf.24... 

The enzyme, 5-dehydroshikimic reductase, converting dehydroshikimic to shikimic acid, has also been studied (964a). It requires triphosphopyri-dinenucleotide as cofactor. 

Dehydroshikimate reductase which reversibly interconverts dehydroshikimate and shikimate is a key enzyme in the biosynthesis of phenolic compounds via the phenylalanine pathway. Phenylalanine ammonia-lyase which catalyzes the cleavage of phenylalanine into transcin-namate and NH3, is equally important for the biosynthesis of phenols. Its activity in tea leaves parallels the content of catechins and epicatechins. 

The reduction of 5-dehydroshikimate to shikimate by partially purified 6-dehydroshikimate reductase has also been studied. A cofactor requirement for reduced triphosphopyridine nucleotide (TPNH) was observed, and the equilibrium constant, at neutral pH, for the reaction... 

In the next step of the sequence, 3-dehydroquinate (4) is dehydrated via a Z-elimination to produce 3-dehydroshiki-mate (5). This reaction is catalyzed by 3-dehydroquinate dehydratase. 3-Dehydroshikimate (5) is, in turn, reduced to shikimate (6) by 3-dehydroshikimate reductase, an enzyme that requires NADPH as a cofactor. Shikimate (6) is then converted to the 3-phosphate (7) by the action of shikimate kinase and ATP. 

Mitsuhashi and Davis 213) also discovered a dehydrogenase that oxidizes quinic acid to dehydroquinic acid in certain mutants of Aerdbactor. In this instance DPN is the required pyridine nucleotide. The bacterial strains that contain this enzyme respond to quinate as a growth factor. This dehydrogenase was purified in the same manner and to about the same extent as dehydroshikimic reductase. The pH optimum of quinic dehydrogenase was found to be at 9.8 Km values obtained were 4.9 X 10" M for quinic acid and 1.4 X 10 M for DPN at pH 9.4. 

At the beginning of 2014, Evolva and IFF announced entering the preproduction phase of natural vanillin by a new de novo process starting from glucose [199] in Schizosaccharomyces pombe, andS. cerevisiae. The engineered pathways involve the incorporation of 3-dehydroshikimate dehydratase from the dung mold Podospora pauciseta, an aromatic carboxylic acid reductase (ACAR) from... 

Next 5-dehydroshikimic acid is reduced to shikimic acid by 5-de-hydroshikimic reductase with TPNH serving as the hydn en donor 214). reaction proceeds according to Eq. (5). 

Purification of the enzyme from extracts of E. coli was carried out by precipitating nucleic acids with MnCU, adsorbing the enzyme on calcium phosphate gel and eluting with phosphate buffer, and then fractionation with (NH4)sS04 between 0.32-0.45 saturation. This procedure produced roughly a tenfold enrichment of enzyme activity. The reductase has its pH optimum at about 8.5. Michaelis constants at pH 8.0 were determined to be 5.5 X 10 M for shikimic acid and 3.1 X 10 M for TPN. (Because of the scarcity of dehydroshikimic acid, the reaction was followed only in the reverse direction.)... 

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