Action of alpha-subunit of G protein is:

Heterotrimeric G proteins are made up of three subunits designated , , and . Both the and the subunits have lipid modifications that anchor these proteins to the plasma membrane. The subunit is bound to GDP. When a ligand binds to a G protein-coupled receptor, this GDP is exchanged for GTP and the subunit separates from the combined and subunits. The separated subunit brings about many biologic effects. The intrinsic GTPase activity of the subunit then conves GTP to GDP, and this leads to reassociation of the with the subunit and termination of effector activation. The GTPase activity of the subunit can be accelerated by a family of regulators of G protein signaling (RGS). Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 2. Overview of Cellular Physiology in Medical Physiology. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.