EC 1.21.3.6     
Accepted name: aureusidin synthase
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
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].
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]
[EC 1.21.3.6 created 2003, modified 2012]
 
 
EC 2.4.1.286     
Accepted name: chalcone 4′-O-glucosyltransferase
Reaction: (1) UDP-α-D-glucose + naringenin chalcone = UDP + 2′,4,4′,6′-tetrahydroxychalcone 4′-O-β-D-glucoside
(2) UDP-α-D-glucose + 2′,3,4,4′,6′-pentahydroxychalcone = UDP + 2′,3,4,4′,6′-pentahydroxychalcone 4′-O-β-D-glucoside
Glossary: naringenin chalcone = 2′,4,4′,6′-tetrahydroxychalcone = 3-(4-hydroxyphemyl)-1-(2,4,6-trihydroxyphenyl)prop-2-en-1-one
Other name(s): 4′CGT
Systematic name: UDP-α-D-glucose:2′,4,4′,6′-tetrahydroxychalcone 4′-O-β-D-glucosyltransferase
Comments: Isolated from the plant Antirrhinum majus (snapdragon). Involved in the biosynthesis of aurones, plant flavonoids that provide yellow color to the flowers.
References:
1.  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]
[EC 2.4.1.286 created 2012]
 
 
EC 2.5.1.136     
Accepted name: 2-acylphloroglucinol 4-prenyltransferase
Reaction: dimethylallyl diphosphate + a 2-acylphloroglucinol = diphosphate + a 2-acyl-4-prenylphloroglucinol
Glossary: naringenin chalcone = 2′,4,4′,6′-tetrahydroxychalcone = 3-(4-hydroxyphemyl)-1-(2,4,6-trihydroxyphenyl)prop-2-en-1-one
phlorisovalerophenone = 3-methyl-1-(2,4,6-trihydroxyphenyl)butan-1-one
Other name(s): PT-1 (gene name); PT1L (gene name); aromatic prenyltransferase (ambiguous)
Systematic name: dimethylallyl diphosphate:2-acylphloroglucinol 4-dimethylallyltransferase
Comments: The enzyme, characterized from hop (Humulus lupulus), acts on phlorisovalerophenone, phlormethylbutanophenone, and phlorisobutanophenone during the synthesis of bitter acids. It also acts with much lower activity on naringenin chalcone. Forms a complex with EC 2.5.1.137, 2-acyl-4-prenylphloroglucinol 6-prenyltransferase, which catalyses additional prenylation reactions. Requires Mg2+.
References:
1.  Tsurumaru, Y., Sasaki, K., Miyawaki, T., Uto, Y., Momma, T., Umemoto, N., Momose, M. and Yazaki, K. HlPT-1, a membrane-bound prenyltransferase responsible for the biosynthesis of bitter acids in hops. Biochem. Biophys. Res. Commun. 417 (2012) 393–398. [PMID: 22166201]
2.  Li, H., Ban, Z., Qin, H., Ma, L., King, A.J. and Wang, G. A heteromeric membrane-bound prenyltransferase complex from hop catalyzes three sequential aromatic prenylations in the bitter acid pathway. Plant Physiol. 167 (2015) 650–659. [PMID: 25564559]
[EC 2.5.1.136 created 2017]
 
 


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