Stone K J
Biochem J. 1976 Jul 1;157(1):105-9. doi: 10.1042/bj1570105.
The reduction of 7,8-dihydrobiopterin to 5,6,7,8-tetrahydrobiopterin by rat liver tetrahydrofolate dehydrogenase (5,6,7,8-tetrahydrofolate-NADP+ oxidoreductase, EC 1.5.1.3) is competitively inhibited by trimethoprim lactate (apparent Ki 0.285 muM). An apparent Michaelis constant of 43 muM for dihydrobiopterin was obtained, which is 430 times higher than the reported Km for dihydrofolate with this enzyme. The reduction of dihydrobiopterin is thus more susceptible to inhibition by trimethoprim lactate than is the reduction of dihydrofolate. However, intraperitoneal administration of trimethoprim had no significant effect on the hepatic supply of tetrahydrobiopterin in rats.
大鼠肝脏四氢叶酸脱氢酶(5,6,7,8-四氢叶酸-NADP+氧化还原酶,EC 1.5.1.3)将7,8-二氢生物蝶呤还原为5,6,7,8-四氢生物蝶呤的过程受到乳酸甲氧苄啶的竞争性抑制(表观Ki为0.285 μM)。测得二氢生物蝶呤的表观米氏常数为43 μM,这比该酶催化二氢叶酸反应时报道的Km值高430倍。因此,二氢生物蝶呤的还原比二氢叶酸的还原更容易受到乳酸甲氧苄啶的抑制。然而,腹腔注射甲氧苄啶对大鼠肝脏四氢生物蝶呤的供应没有显著影响。