Catalyzes the conversion of 4-hydroxyphenylpyruvic acid to homogentisic acid, one of the steps in tyrosine catabolism. 3-(4-hydroxyphenyl)pyruvate + O2 = CO2 + homogentisate Binds 1 Fe cation per subunit. Amino-acid degradation; L-phenylalanine degradation; acetoacetate and fumarate from L-phenylalanine: step 3/6. Homodimer. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the 4HPPD family.