4-Hydroxyphenylpyruvate dioxygenase (HPPD), also known as α-ketoisocaproate dioxygenase (KIC dioxygenase), is an Fe (II)-containing non-heme oxygenase that catalyzes the second reaction in the catabolism of tyrosine - the conversion of 4-hydroxyphenylpyruvate into homogentisate. HPPD also catalyzes the conversion of phenylpyruvate to 2-hydroxyphenylacetate and the conversion of α-ketoisocaproate to β-hydroxy β-methylbutyrate.HPPD is an enzyme that is found in nearly all aerobic forms of life.[In nearly all aerobic beings, 4- Hydroxyphenylpyruvate dioxygenase is responsible for converting 4- Hydroxyphenylpyruvate into homogentisate.This conversion is one of many steps in breaking L-tyrosine into acetoacetate and fumarate.While the overall products of this cycle are used to create energy, plants and higher order eukaryotes utilize HPPD for a much more important reason. In eukaryotes, HPPD is used to regulate blood tyrosine levels, and plants utilize this enzyme to help produce the cofactors plastoquinone and tocopherol which are essential for the plant to survive.