An enzyme designated as NADPH-dihydropteridine reductase was found in the extract of bovine liver and partially purified. In contrast to NADH-dependent dihydropteridine reductase [EC 1. 6. 99. 7], the enzyme catalyzes the reduction of quinonoid-dihydropterin' to tetrahydropterin in the presence of NADPH. The two enzymes were separated by column chromatography on DEAE-Sephadex. Tyrosine formation in the phenylalanine hydroxylation system was also stimulated by NADPH-dihydropteridine reductase. The existence of these two dihydropteridine reductases suggests that the tetrahydro form of pteridine cofactor may be regenerated in two different ways in vivo.
The Japanese Biochemical Society