naringenin-chalcone and aureusidin

Aureusidin synthase, which plays a key role in the yellow coloration of snapdragon flowers, is a homolog of plant polyphenol oxidase (PPO). The enzyme specifically acted on chalcones with a 4-monohydroxy or 3,4-dihydroxy B-ring to produce aurones, for whose production the oxidative cyclization of chalcones must be preceded by 3-oxygenation. However, it exhibited virtually no PPO activity toward non-chalcone phenolics. The enzyme was competitively inhibited by phenylthiourea, a specific PPO inhibitor. These results led us to propose a mechanism of aurone synthesis by aureusidin synthase on the basis of known PPO-catalyzed reactions and conclude that the enzyme is a chalcone-specific PPO specialized for aurone biosynthesis.

Topics: Benzofurans; Catechol Oxidase; Chalcone; Chalcones; Enzyme Inhibitors; Magnoliopsida; Mixed Function Oxygenases; Models, Molecular; Molecular Conformation; Pigmentation; Plant Structures; Substrate Specificity