Involved in the catabolism of homogentisate (2,5-dihydroxyphenylacetate or 2,5-OH-PhAc), a central intermediate in the degradation of phenylalanine and tyrosine. Catalyzes the oxidative ring cleavage of the aromatic ring of homogentisate to yield maleylacetoacetate. homogentisate + O2 = 4-maleylacetoacetate + H(+) Amino-acid degradation; L-phenylalanine degradation; acetoacetate and fumarate from L-phenylalanine: step 4/6. Hexamer; dimer of trimers. By nitrogen and carbon deprivation as well as in the presence of tyrosine. Also induced by phenylalanine, but only in nitrogen-free medium. Mutant is unable to use tyrosine as carbon source, lacks homogentisate dioxygenase activity, produces a melanin-like pigment and is affected in stationary-phase survival. Belongs to the homogentisate dioxygenase family.