Labeled Nitisinone. Nitisinone is a herbicidal triketone that inhibits 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme involved in plastoquinone biosynthesis in plants and in tyrosine catabolism in mammals. It is used in treatment of inherited tyrosinemia type I.Form:Tan SolidMelting Point:132-134°CSolubility:Chloroform, Ethyl Acetate