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. Produces mainly (S)-betalamic acid. L-dopa + O2 = 4-(L-alanin-3-yl)-2-hydroxy-cis,cis-muconate 6-semialdehyde + H(+) Binds 1 zinc ion per subunit. kcat is 0.095 sec(-1) for L-dopa. Optimum pH is 8.5. Pigment biosynthesis; betalain biosynthesis. Monomer. Supplementation with Fe(2+) in the reaction medium is not necessary to detect activity in contrast to the results found for the M. jalapa enzyme (AC B6F0W8) (PubMed:22270561). Belongs to the DODA-type extradiol aromatic ring-opening dioxygenase family.