(1) ligand binds to receptor, altering its conformation and increasing its affinity for the G protein to which it binds- In GTP bound conformation, the Ga subunit has a low affinity for Gby
(2) the Ga subunit releases its GDP, which is replaced by GTP
(3) the Ga subunit dissociates from the Gby complex and binds to an effector (may be adenylyl cyclase) (others include C-B and cyclic GMP phosphodiesterase), activating the effector. The Gby dimer may also bind to an effector, such as (PLCb, K+ ion channels, adenylyl cyclase, and PI 3-kinase)
(4) activated adenylyl cyclase produced cAMP- second messenger.
(5) the GTPase activity of Ga hydrolyzes the bound GTP, deactivating Ga- this results in a conformation change causing a decrease in affinity for the effector and an increase in affinity for the by subunit
(6) Ga reassociates with Gby, reforming the trimeric G protein, and the effector ceases its activity.
(7) the receptor has been phosphorylated by a GRK
(8) the phosphorylated receptor has been bound by an arrestin molecule, which inhibits the ligand-bound receptor from activating additional G proteins. The receptor bound to arrestin is likely to be taken up by endocytosis.