Involved in the biosynthesis of the enediyne antitumor antibiotic C-1027. Catalyzes the MIO-dependent deamination of L-tyrosine generating the corresponding alpha,beta-unsaturated acid, (S)-beta-tyrosine. L-tyrosine = 3-amino-3-(4-hydroxyphenyl)propanoate L-tyrosine = (E)-4-coumarate + NH4(+) Homotetramer; dimer of dimers. Contains an active site 4-methylidene-imidazol-5-one (MIO), which is formed autocatalytically by cyclization and dehydration of residues Ala-Ser-Gly. Belongs to the TAL/TAM family.