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 2,5-dihydroxyphenylacetate 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. Induced by homogentisate and repressed by HmgR. Cells lacking this gene are unable to grow in medium containing phenylalanine or tyrosine as the sole carbon sources, and accumulate homogentisate. Belongs to the homogentisate dioxygenase family.