Has aminomutase and, to a much lesser extent, ammonia-lyase activity. Primarily, catalyzes the rearrangement of L-tyrosine to S-beta-tyrosine, which is probably incorporated into secondary metabolite myxovalargin. The aminomutase activity exclusively produces 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.