Abstract
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.
MeSH terms
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Benzofurans / chemistry
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Benzofurans / metabolism*
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Catechol Oxidase / antagonists & inhibitors
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Catechol Oxidase / chemistry
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Catechol Oxidase / metabolism*
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Chalcone / analogs & derivatives
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Chalcone / chemistry
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Chalcone / metabolism
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Chalcones
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Enzyme Inhibitors / pharmacology
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Magnoliopsida / enzymology*
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Magnoliopsida / metabolism
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Mixed Function Oxygenases / antagonists & inhibitors
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Mixed Function Oxygenases / chemistry
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Mixed Function Oxygenases / isolation & purification
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Mixed Function Oxygenases / metabolism*
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Models, Molecular
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Molecular Conformation
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Pigmentation*
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Plant Structures / enzymology
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Plant Structures / metabolism*
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Substrate Specificity
Substances
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Benzofurans
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Chalcones
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Enzyme Inhibitors
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aureusidin
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Chalcone
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naringenin chalcone
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Mixed Function Oxygenases
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aureusidin synthase
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Catechol Oxidase