ID 1.21.3.6 DE aureusidin synthase. CA (1) 2',4,4',6'-tetrahydroxychalcone 4'-O-beta-D-glucoside + H(+) + O2 = CA aureusidin 6-O-beta-glucoside + H2O. CA (2) 2 2',3,4,4',6'-pentahydroxychalcone 4'-O-beta-D-glucoside + 2 H(+) + CA O2 = 2 aureusidin 6-O-beta-glucoside + 2 H2O. CA (3) 2',3,4,4',6'-pentahydroxychalcone 4'-O-beta-D-glucoside + H(+) + O2 = CA bracteatin 6-O-beta-glucoside + H2O. CC -!- Plays a key role in the yellow coloration of flowers such as CC Antirrhinum majus (snapdragon). CC -!- The enzyme is a homolog of plant polyphenol oxidase and catalyzes two CC separate chemical transformations, i.e. 3-hydroxylation and oxidative CC cyclization (2',-dehydrogenation). CC -!- H2O2 activates reaction (1) but inhibits reaction (2). CC -!- Originally considered to act on the phenol but now thought to mainly CC act on the 4'-O-beta-glucoside in vivo. DR Q9FRX6, AS1_ANTMA ; //