Energy Coupling Nicotinate Phosphoribosyltransferase

烟酸磷酸核糖基转移酶水解1个ATP分子 对于NAMN形成的每个周期，这两个过程是 能量耦合。 一种新的交替亲和机制， 提出了这种耦合，其中ATP的使用产生了E-P， 增加的对底物的亲和力 磷酸核糖基转移酶反应;磷酸核糖基后 转移，产品引发的强制性E-P水解 焦磷酸盐再生低亲和力E型， 产品发布 一个E-P被证明是机械参与 在偶联中，将使用ADP/ATP交换和蛋白质化学 磷酸化残基的突变将 允许解偶联的ATP酶和NAMN合成活动的 酵素 将进行立体化学研究，以确定 如果存在其它磷酸化中间体。 E-P有 显著降低底物PRPP的Km值， 烟酸酯，与E相比，并使用进一步的结合研究 将量化E-P形成的变化。 快速 淬火研究将允许确定的顺序E-P 水解和磷酸核糖基转移。 通过 学习NAPRTase中能量耦合的机制。 这将 显示了亲和力的改变如何导致更多的偶联， 复杂系统如Ca-ATP酶和其他载体转运蛋白。

Nicotinate phosphoribosyltransferase hydrolyzes 1 molecule of ATP for each cycle of NAMN formation, and the two processes are energetically coupled. A novel alternating affinity mechanism is proposed for this coupling in which ATP use generates an E-P with increased affinity for the substrates of the phosphoribosyltransferase reaction; after phosphoribosyl group transfer, compulsory E-P hydrolysis triggered by product pyrophosphate regenerates the low affinity E form and results in product release. An E-P was shown to be mechanistically involved in coupling, ADP/ATP exchanges and protein chemistry will be used to characterize it. Mutagenesis at the phosphorylated residue will allow uncoupling the ATPase and NAMN synthesis activities of the enzyme. Stereochemical studies will be carried out to determine if other phosphorylated intermediates exist. The E-P has dramatically decreased Km values for substrates PRPP and nicotinate, compared to E, and the use of further binding studies will quantitate the changes that occur on E-P formation. Rapid quench studies will allow the determination the order of E-P hydrolysis and phosphoribosyl group transfer in the mechanism. By learning the mechanism of energy coupling in NAPRTase. This will show how alternation in affinity can lead to coupling in more complex systems such Ca-ATPase and other vectorial transporters.