Carbonyl reductase activity of sepiapterin reductase from rat erythrocytes

A homogeneous preparation of sepiapterin reductase, an enzyme involved in the biosynthesis of tetrahydrobiopterin, from rat erythrocytes was found to be responsible for the reduction with NADPH of various carbonyl compounds of non-pteridine derivatives including some vicinal dicarbonyl compounds which were reported in the previous paper (Katoh, S. and Sueoka, T. (1984) Biochem, Biophys. Res. Commun. 118, 859-866) in addition to the general substrate, sepiapterin (2-amino-4-hydroxy-6-lactoyl-7,8-dihydropteridine). The compounds sensitive as substrates of the enzyme were quinones, e.g., p-quinone and menadione; other vicinal dicarbonyls, e.g., methylglyoxal and phenylglyoxal; monoaldehydes, e.g., p-nitrobenzaldehyde; and monoketones, e.g., acetophenone, acetoin, propiophenone and benzylacetone. Rutin, dicoumarol, indomethacin, and ethacrynic acid inhibited the enzyme activity toward either a carbonyl compound of a non-pteridine derivative or sepiapterin as substrate. Sepiapterin reductase is quite similar to general aldo-keto reductases, especially to carbonyl reductase.