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. Cofactor biosynthesis; prenylquinone biosynthesis. Homodimer. A number of isoforms are produced. According to EST sequences. Belongs to the 4HPPD family. Extended N-terminus.