The enzymatic synthesis of sepiapterin by chicken kidney preparations.

A chicken kidney preparation which catalyzes the conversion of D-erythro-dihydroneopterin triphosphate to dihydrobiopterin in the presences of Mg2+ and NADPH has been fractionated into three fractions, A2, A1, and B. Fraction A2 in the presence of Mg2+ catalyzes the conversion of D-erythro-dihydroneopterin triphosphate to an unknown intermediate designated compound X. Fraction A1 in the presence of NADPH catalyzes the conversion of compound X to sepiapterin. Fraction B, in the presence of NADPH, catalyzes the conversion of sepiapterin to dihydrobiopterin. Fraction B which is sepiapterin reductase was not studied any further. Fraction A1 is heat-labile and its molecular weight is estimated to be 3.0 x 10(4), whereas fraction A2 is heat-stable and its molecular weight, 7.7 x 10(4). Compound X is labile and its degradation products have been identified to be pterin and pyruvic acid. This information suggests that compound X is 6-(1,2-dioxopropyl)-7,8-dihydropterin.