Partial purification and some properties of biopterin synthase and dihydropterin oxidase from Drosophila melanogaster

Abstract

An enzyme which has been named "biopterin synthase" has been discovered in Drosophila melanogaster. This enzyme, which has been purified 200-fold from extracts of Drosophila, catalyzes the conversion of sepiapterin to dihydrobiopterin, or oxidized sepiapterin to biopterin. The Km values for the two substrates are 63 microM for sepiapterin and 10 microM for oxidized sepiapterin. NADPH is required in this enzymatic reaction. An analysis of enzyme activity during development in Drosophila indicates a correlation between enzyme activity and biopterin content at various development stages. Another enzyme, called "dihyropterin oxidase," was also discovered and partially purified. This enzyme catalyzes the oxidation of dihydropterin compounds to the corresponding pterin compounds. For example, sepiapterin (a dihydroterin) is oxidized to oxidized sepiapterin in the presence of this enzyme. The only dihydropterin that has been tested that is not a substrate for this enzyme is dihydroneopterin triphosphate, the compound thought to be a precursor for all naturally occurring pterins and dihydropterins. Since the action of dihydropterin oxidase is reduced significantly when the concentration of oxygen is very low, it is likely that this enzyme uses molecular oxygen as the oxidizing agent during the oxidation of dihydropterins. Neither NAD+ or NADP+ is required. In the presence of the two enzymes dihydropterin oxidase and biopterin synthase, sepiapterin is converted to biopterin. However, in the presence of biopterin synthase alone, sepiapterin is converted to dihydrobiopterin.

Biosynthesis of Pteridines in Insects: A Review

“…The oxidation of 7,8-dihydropterin to pterin was shown to be catalyzed by the enzyme dihydropterin oxidase. This enzyme was first purified from D. melanogaster and, though it can use many 7,8-dihydropterin compounds as substrates, the biochemical parameters indicated that its physiological role in D. melanogaster was to participate in the synthesis of isoxanthopterin [40,41] (Figure 6). Among all the D. melanogaster eye-color mutants analyzed, only little isoxanthopterin (lix) did not show any detectable dihydropterin oxidase activity [42].…”

“…The oxidation of 7,8-dihydroxanthopterin to the yellow pigment xanthopterin is most likely catalyzed by the enzyme dihydropterin oxidase. This enzyme was first purified from D. melanogaster and was shown to be able to use many 7,8-dihydropterin compounds as substrates [40,41].…”