Metabolism of the Phenylalanine Hydroxylation Cofactor

Abstract

Abstract A simple chemical method of reducing biopterin to 7,8-dihydrobiopterin has been described. The product of this reaction appears to be identical with the phenylalanine hydroxylation cofactor isolated from rat liver extracts. With the use of the synthetic compound, the TPNH-mediated enzymatic reduction of dihydrobiopterin to the tetrahydro level has been demonstrated. This reduction is catalyzed by dihydrofolate reductase. In the presence of 7,8-dihydrobiopterin, the reductase is an essential component of the phenylalanine-hydroxylating system. The TPN-dependent oxidation of dihydrobiopterin to sepiapterin has been shown to be catalyzed by another enzyme, sepiapterin reductase.