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Mechanism Of The Hydroxylation Reactions Catalyzed By 4-Hydroxyphenylpyruvate Dioxygenase And Hydroxymandelate Synthase, Dhara D. Shah
Mechanism Of The Hydroxylation Reactions Catalyzed By 4-Hydroxyphenylpyruvate Dioxygenase And Hydroxymandelate Synthase, Dhara D. Shah
Theses and Dissertations
4-Hydroxyphenylpyruvate dioxygenase (HPPD) and Hydroxymandelate synthase (HMS) carry out highly similar complex dioxygenation reactions using the substrates, 4-hydroxyphenylpyruvate (HPP) and dioxygen. HPPD catalyzes decarboxylation, aromatic hydroxylation and substituent migration (NIH shift) in a single catalytic cycle to form homogentisate (HG), whereas HMS catalyzes decarboxylation and aliphatic hydroxylation to give hydroxymandelate (HMA). Wild-type HPPD, HPPD variants and HMS variants produce both native and non-native products. Based on this observation, we have employed a product analysis method with HPP deuterium substitutions (ring or benzylic) that reveal kinetic isotope effects from intermediate partitioning ratios. In this study we offer evidence for the 1) …