Abstract
The conversion of sepiapterin by pterine reductase obtained from Drosophila melanogaster was investigated biochemically. Molar ratio of reduced triphosphopyridine nucleotide as a cofactor to sepiapterin as a substrate on this enzymatic reaction, was 1.0. The spectra of the reaction product were very similar to those of tetrahydropteridine. These facts suggest that the reaction product is tetrahydrosepiapterin.
The products further converted from the tetrahydrosepiapterin by non-enzymatic oxidation were analyzed biochemically. In the absence of oxygen, the main product, compound A, was indistinguishable from biopterin in the chemical natures examined. In the presence of oxygen, the products of 2-amino-4-hydroxypteridine and 2-amino-4-hydroxypteridine.6-carboxylic acid were confirmed.
From these experimental results, the metabolic relationships among pteridine derivatives found in Drosophila were clarified. A plausible scheme of pteridine metabolism is as follows:
Sepiapterin_??_Tetrahydrosepiapterin_??_[Dihydrobiopterin]_??_Biopterin
2-amino-4-hydroxypteridine
