Hpd, also known as 4-hydroxyphenylpyruvate dioxygenase, is a Fe-containing enzyme that catalyzes the second reaction in the catabolism of tyrosine the conversion of 4-hydroxyphenylpyruvate to homogentisate. Existing as a homodimer, Hpd uses zinc as a cofactor to catalyze the third step in the conversion of L-phenylalanine to fumarate and acetoacetic acid. Defects in the gene encoding Hpd are the cause of tyrosinemia type 3 and hawkinsinuria, both of which are inborn errors of metabolism that are associated with a variety of symptoms, including mental retardation and seizures and hair and urine abnormalities. Recombinant mouse Hpd protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.