EFFECTS OF METAL IONS ON THE INTRINSIC GTP-HYDROLYSIS ACTIVITIES OF SMALL GTPase Cdc42Hs
金属离子对GTP结合蛋白Cdc42Hs的内源性GTP酶活性的影响

Different metal ions have different effects on the intrinsic GTP-hydrolysis activity of Cdc42Hs. Compared with Mg2 , the physiological cofactor, Mn2 has a slight activation effect on GTP-hydrolysis activity. The kobs of the exponential phase of the experiment curve of Mn2 is two-times higher than that of Mg2 under saturated condition. And the velocity of the steady state is lower than that of Mg2 . Essentially, there is no difference between the experiment curves of Mn2 and Mg2 . Both of them have an exponential phase and linear phase, which indicate that Mn2 and Mg2 adopt the same mechanism in binding to Cdc42Hs. In the case of Ca2 , there is no detectable exponential phase in the experiment curve. The presence of Ca2 only slows down the velocity of the steady state. This indicates that the binding mechanism of Ca2 to Cdc42Hs is different from that of Mn2 and Mg2 . With the increasing of Mn2 and Mg2 concentration, the kobs of the exponential phase increase, and the velocity of the steady state decrease. A detail kinetic analysis deduces the microscopic kinetic constants of the hydrolysis reaction and the disassociate constants of the metal ions with the protein.