Purification of dihydropteridine reductase from human platelets

Dihydropteridine reductase was purified approximately 1,700-fold from human outdated blood platelets. Two forms of the enzyme, A and B, were resolved. They have the same Km values for 2-amino-6,7,-dimethyl-4-hydroxydihydropteridine (46 microM vs 49 microM), but the A form has a Km for NADH that is two times higher than that of the B form (20 microM vs 9 microM).