Reaction: (1) 2',4,4',6'-tetrahydroxychalcone 4'-O-β-D-glucoside + O2 = aureusidin 6-O-β-D-glucoside + H2O
(2) 2',3,4,4',6'-pentahydroxychalcone 4'-O-β-D-glucoside + ½ O2 = aureusidin 6-O-β-D-glucoside + H2O
(3) 2',3,4,4',6'-pentahydroxychalcone 4'-O-β-D-glucoside + O2 = bracteatin 6-O-β-D-glucoside + H2O
For diagram of reaction click here.
Glossary: 2',4,4',6'-tetrahydroxychalcone = 3-(4-hydroxyphenyl)-1-(2,4,6-trihydroxyphenyl)prop-2-en-1-one
aureusidin = 4,6-dihydroxy-2-[(3,4-dihydroxyphenyl)methylidene]benzofuran-3(2H)-one
bracteatin = 4,6-dihydroxy-2-[(3,4,5-trihydroxyphenyl)methylidene]benzofuran-3(2H)-one
Other name(s): AmAS1
Systematic name: 2',4,4',6'-tetrahydroxychalcone 4'-O-β-D-glucoside:oxygen oxidoreductase
Comments: A copper-containing glycoprotein that plays a key role in the yellow coloration of flowers such as Antirrhinum majus (snapdragon). The enzyme is a homologue of plant polyphenol oxidase [1] and catalyses two separate chemical transformations, i.e. 3-hydroxylation and oxidative cyclization (2',-dehydrogenation). H2O2 activates reaction (1) but inhibits reaction (2). Originally considered to act on the phenol but now thought to act mainly on the 4'-O-β-D-glucoside in vivo [4].
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number: 320784-48-3
References:
1. Nakayama, T., Yonekura-Sakakibara, K., Sato, T., Kikuchi, S., Fukui, Y., Fukuchi-Mizutani, M., Ueda, T., Nakao, M., Tanaka, Y., Kusumi, T. and Nishino, T. Aureusidin synthase: A polyphenol oxidase homolog responsible for flower coloration. Science 290 (2000) 1163-1166. [PMID: 11073455]
2. Nakayama, T., Sato, T., Fukui, Y., Yonekura-Sakakibara, K., Hayashi, H., Tanaka, Y., Kusumi, T. and Nishino, T. Specificity analysis and mechanism of aurone synthesis catalyzed by aureusidin synthase, a polyphenol oxidase homolog responsible for flower coloration. FEBS Lett. 499 (2001) 107-111. [PMID: 11418122]
3. Sato, T., Nakayama, T., Kikuchi, S., Fukui, Y., Yonekura-Sakakibara, K., Ueda, T., Nishino, T., Tanaka, Y. and Kusumi, T. Enzymatic formation of aurones in the extracts of yellow snapdragon flowers. Plant Sci. 160 (2001) 229-236. [PMID: 11164594]
4. Ono, E., Fukuchi-Mizutani, M., Nakamura, N., Fukui, Y., Yonekura-Sakakibara, K., Yamaguchi, M., Nakayama, T., Tanaka, T., Kusumi, T. and Tanaka, Y. Yellow flowers generated by expression of the aurone biosynthetic pathway. Proc. Natl. Acad. Sci. USA 103 (2006) 11075-11080. [PMID: 16832053]