Determination of quinonoid dihydrobiopterin by liquid chromatography and electrochemical detection.

Tetrahydrobiopterin (BH4) is a required cofactor for the hydroxylation of the amino acids phenylalanine, tyrosine and tryptophan. Quinonoid dihydrobiopterin (q-BH2) is the natural product of the oxidation of BH4 in these enzymatic reactions. This report describes a method based on liquid chromatography and electrochemical detection for the determination of q-BH2 in synthetic and biological samples. This methodology is used to study the electrochemistry of q-BH2 formed by oxidation of BH4 and in the hydroxylation of phenylalanine by phenylalanine hydroxylase.