Opens the cyclic ring of dihydroxy-phenylalanine (DOPA) between carbons 4 and 5, thus producing an unstable seco-DOPA that rearranges nonenzymatically to betalamic acid. L-dopa + O2 = 4-(L-alanin-3-yl)-2-hydroxy-cis,cis-muconate 6-semialdehyde + H(+) Binds 1 zinc ion per subunit. Pigment biosynthesis; betalain biosynthesis. Expressed only in colored petals and pigmented tissues, absent from green stems and leaves. Very high expression in immature colored petals, then decreases in mature colored petals. In contrary to the fungal dioxygenase (AC P87064), this enzyme does not have a significant 2,3-ring-cleaving activity. Belongs to the DODA-type extradiol aromatic ring-opening dioxygenase family.