Probable reaction mechanisms of flavokinase and FAD synthetase from rat liver.
Probable reaction mechanisms of flavokinase and FAD synthetase from rat liver.
复制标题
大鼠肝脏黄素激酶和 FAD 合成酶的可能反应机制。
DOI：
10.1016/0003-9861(90)90240-y
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发表时间：
1990
影响因子：
3.9
通讯作者：
McCormick,DB
中科院分区：
文献类型：
--
作者：
Yamada,Y;MerrillJr,AH;McCormick,DB
用纯化的大鼠肝脏黄素激酶和FAD合成酶进行了稳态动力学分析和产物抑制评价。核黄素的Km值约为11μm，ATP的Km值约为3.7μm；核黄素的Km值为6μm，核黄素的Km值为120μm，锌的Km值为23μm。从抑制模式来看，黄酮激酶反应遵循有序的双双机制，核黄素首先结合，然后是三磷酸腺苷；ADP首先释放，然后是FMN。FAD合成酶的Km值分别为9.1μm和71μm，Km值分别为0.75μm和1.3μm，焦磷酸盐的Km值为66μm。产物抑制模式表明，FAD合成酶反应也遵循有序的双双机理，其中ATP先于FMN与酶结合，焦磷酸在FAD之前从酶中释放。将Ki值与FMN和FAD的生理浓度进行比较，表明FAD的生物合成很可能是在FAD合成酶反应阶段作为产物受到这种辅酶的调节。
A steady-state kinetic analysis with evaluation of product inhibition was accomplished with purified rat liver flavokinase and FAD synthetase. For flavokinase,Kmvalues were calculated as approximately 11 μmfor riboflavin and 3.7 μmfor ATP.Kivalues were calculated for FMN as 6 μmagainst riboflavin and for ZnADP as 120 μmagainst riboflavin and 23 μmagainst ZnATP. From the inhibition pattern, the flavokinase reaction followed an ordered bi bi mechanism in which riboflavin binds first followed by ATP; ADP is released first followed by FMN. For FAD synthetase,Kmvalues were calculated as 9.1 μmfor FMN and 71 μmfor MgATP.Kivalues were calculated for FAD as 0.75 μmagainst FMN and 1.3 μmagainst MgATP and for pyrophosphate as 66 μmagainst FMN. The product inhibition pattern suggests the FAD synthetase reaction also followed an ordered bi bi mechanism in which ATP binds to enzyme prior to FMN, and pyrophosphate is released from enzyme before FAD. Comparison ofKivalues with physiological concentrations of FMN and FAD suggests that the biosynthesis of FAD is most likely regulated by this coenzyme as product at the stage of the FAD synthetase reaction.