Specificity analysis and mechanism of aurone synthesis catalyzed by aureusidin synthase, a polyphenol oxidase homolog responsible for flower coloration

Aureusidin synthase, which plays a key role in the yellow coloration of sna pdragon flowers, is a homolog of plant polyphenol oxidase (PPO), The enzyme specifically acted on chalcones with a il-monohydroxy or 3,4-dihydroxy B-r ing to produce aurones, for whose production the oxidative cyclization of c halcones must be preceded by 3-osygenation, However, it exhibited virtually no PPO activity toward non-chalcone phenolics. The enzyme was competitivel y inhibited by phenylthiourea, a specific PPO inhibitor. These results led us to propose a mechanism of aurone synthesis by areusidin synthase on the basis of known PPO-catalyzed reactions and conclude that the enzyme is a ch alcone-specific PPO specialized for aurone biosynthesis. (C) 2001 Federatio n of European Biochemical Societies. Published by Elsevier Science B,V, All rights reserved.