dihydrobiopterin

di·hy·dro·bi·op·ter·in

(dī-hī'drō-bī-op'tĕr-in), Precursor to tetrahydrobiopterin, a required cofactor for a number of enzymes, including the biosynthesis of l-tyrosine; the inability to synthesize dihydrobiopterin can result in a form of malignant hyperphenylalaninemia.