<unk> s, or<unk> s, or<unk>  Accelerating<unk> s is a family of regulatory<unk> s whose members can bind to activated G<unk> s and stimulate their<unk>  activity with the result of terminating the signaling event.<unk> s mediate switching a G<unk>  on and off. G<unk> s are switched from the active, GTP-bound form to the inactive, GDP-bound form by hydrolysis of the GTP through intrinsic<unk> -activity. It can be reverted (switching the G<unk>  on again) by guanine nucleotide exchange factors (GEFs). Only the active state of the G<unk>  can transduce a signal to a reaction chain.
The ability of<unk> s to turn off G<unk> s 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<unk> s or specific lipids, or by phosphorylation.
The<unk> s that act on small GTP-binding<unk> s of the Ras superfamily have conserved structures and use similar mechanisms, whereas most of those that act on alpha subunits of heterotrimeric G<unk> s belong to a distinct family, the RGS<unk>  family.
An example of a<unk>  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<unk> s into the cell.  Ran is turned on or off by GEFs and<unk> s, respectively.
GTPase activating protein
Receptor tyrosine kinase
Rho GTPase
Serine/threonine-specific protein kinase
Adenylate cyclase
Guanine nucleotide exchange factor
Cyclin-dependent kinase
Adenylate kinase