(hō'mō-jen'tis-āt dī-oks'i-jen-ās), An iron-containing enzyme that catalyzes the oxidative cleavage of the benzene ring in homogentisic acid by O2, forming 4-maleylacetoacetate; an absence or deficiency of this enzyme will result in alcaptonuria. Synonym(s): homogentisic acid oxidase