Studies on sepiapterin reductase: Further characterization of the reaction product

Abstract

Sepiapterin reductase from rat liver catalyzes reduction of sepiapterin in the presence of NADPH. The reaction product was isolated from the reaction mixture via Sephadex column chromatography and its properties were compared with those of synthetic dihydrobiopterin. All of the chemical and enzymatic characteristics examined distinctly indicated that two compounds are identical. Stoichiometry of sepiapterin reductase-catalyzed reaction was established from balance studies. Evidence is presented which indicates that dihydrobiopterin will be reduced to tetrahydrobiopterin by dihydrofolate reductase in the presence of NADPH. Stoichiometric formulation was proposed for the enzymatic reduction of dihydrobiopterin. From spectral characteristics and behaviors toward enzymatic reduction, a possibility of 7,8-dihydro structure of dihydrobiopterin has been discussed.