Plays a role in the tyrosine degradation pathway. homogentisate + O2 = 4-maleylacetoacetate + H(+) Amino-acid degradation; L-phenylalanine degradation; acetoacetate and fumarate from L-phenylalanine: step 4/6. Expressed in the hypodermis and intestine. RNAi-mediated knockdown together with fah-1 RNAi rescues the impaired growth and fertility defects in the single fah-1 RNAi mutant. Belongs to the homogentisate dioxygenase family.