Pyruvylshikimate 3-phosphate

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).

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. 

D.B. SPRINSON. 1971. On the mechanism of 5-enol-pyruvylshikimate 3-phosphate synthetase. J. Biol. Chem. 246 6191-6196. 

Binding of fully oxidized FMN to enzyme was considerably enhanced in the presence of substrate, while a smaller enhancement was observed with product, leading the authors to suggest that a ternary enzyme-FMN-(substrate/product) complex is formed. Reduction of FMN in the presence of enzyme resulted in the formation of fully reduced, enzyme-bound, flavin. When FMN was reduced in the presence of both enzyme and the substrate analogue (6R)-6-fluoro-5-enol-pyruvylshikimate-3-phosphate a neutral flavin radical was formed. The radical was also formed to a lesser extent in the presence of 5-enolpyruvylshikimate-3-phosphate (40%) and chorismate (14%). 

EPR showed that the radical had g = 2.0039 and a linewidth of 2.1 mT which decreased to 1.5 mT in deuterated buffer, consistent with a neutral flavin radical. The linewidth was independent of whether chorismate or (6R)-6-fluoro-5-enol-pyruvylshikimate-3-phosphate was present. 

Transition-state analysis has been reported for acid-catalysed hydrolysis of the enol ether functionality of enol pyruvylshikimate 3-phosphate for which rate-determining C(3) protonation precedes attack of H2O 2- " C, 3- " C, 3,3- H2, and solvent deuterium KIEs have been discussed." " ... 

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