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. Regulated by MYB1. Belongs to the DODA-type extradiol aromatic ring-opening dioxygenase family.