Dihydropteridine reductase and tetrahydropterin in Crithidia fasciculata cells

Dihydropteridine reductase was found in extracts of Crithidia fasciculata and was demonstrated by the fact that the enzyme required both quinonoid-dihydropterin and NADH as substrates. 7,8-Dihydropterin and dihydrofolate failed to serve as substrates; tetrahydropterin was formed as the reaction product. The molecular weight of the enzyme was estimated to be about 55 000 by Sephadex G-100 gel filtration. NADH was more effective than NADPH as substrate for the enzyme. Tetrahydropterin (1.35 nmol tetrahydrobiopterin equivalents/g cells) was also detected in C. fasciculata.