( ) The cycling of G protein between active and inactive states is aided by accessory proteins that bind to the G protein.What accessory protein accounts for switch off of G protein?A.GEFs (Guanine nucleotide-exchange factors)B.GDIs (Guanine nucleoti

( ) The cycling of G protein between active and inactive states is aided by accessory proteins that bind to the G protein.What accessory protein accounts for switch off of G protein?A.GEFs (Guanine nucleotide-exchange factors)B.GDIs (Guanine nucleoti
( ) The cycling of G protein between active and inactive states is aided by accessory proteins that bind to the G protein.What accessory protein accounts for switch off of G protein?
A.GEFs (Guanine nucleotide-exchange factors)
B.GDIs (Guanine nucleotide-dissociation inhibitors)
C.GAPs (GTPase-activating proteins)
D.phosphatases

( ) The cycling of G protein between active and inactive states is aided by accessory proteins that bind to the G protein.What accessory protein accounts for switch off of G protein?A.GEFs (Guanine nucleotide-exchange factors)B.GDIs (Guanine nucleoti
GTPase Activating Proteins,or GAPs,or GTPase Accelerating Proteins is a family of regulatory proteins whose members can bind to activated G proteins and stimulate their GTPase activity with the result of terminating the signaling event.
GAPs mediate switching a G protein on and off.G proteins are switched from the active,GTP-bound form to the inactive,GDP-bound form by hydrolysis of the GTP through intrinsic GTPase-activity.It can be reverted (switching the G protein on again) by guanine nucleotide exchange factors (GEFs).Only the active state of the G protein can transduce a signal to a reaction chain.
The ability of GAPs to turn off G proteins depends on their local concentration in the cell,and on their own activity state.Both of these are frequently under regulation of one or more signaling pathways,and modified by binding to other regulatory proteins or specific lipids,or by phosphorylation.
The GAPs that act on small GTP-binding proteins of the Ras superfamily have conserved structures and use similar mechanisms,whereas most of those that act on alpha subunits of heterotrimeric G proteins belong to a distinct family,the RGS protein family.
An example of a GTPase is the monomer,Ran,which is found in the cytosol as well as the nucleus.Hydrolysis of GTP by Ran is thought to provide the energy needed to transport nuclear proteins into the cell.Ran is turned on or off by GEFs and GAPs,respectively.
希望能够对你有所帮助.

选C,GAP可以活化G蛋白alpha基的GTPase活性，使GTP水解为GDP,G蛋白失活，也就是开关关闭即switch off

选B
因为GDIs的作用是抑制结合的GDP从G蛋白释放出来, 所以GDIs可保持G蛋白处于非活性状态，也就是switch off状态。