Final answer:
Signaling by an activated Gα subunit is terminated by the hydrolysis of GTP to GDP, deactivating the subunit and leading it to re-associate with the β and γ subunits.
Step-by-step explanation:
The process by which signaling by an activated Gα subunit is terminated involves hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP). This mechanism occurs after the G-protein-coupled receptor (GPCR) has been activated by a ligand leading to the exchange of GDP for GTP on the Gα subunit. The GTP-bound Gα subunit is active and can propagate the signal by activating downstream effectors.
Eventually, the intrinsic GTPase activity of the Gα subunit hydrolyzes the GTP to GDP, which leads to deactivation of the signaling. Subsequently, the Gα subunit re-associates with the β and γ subunits, returning to its inactive state and completing the cycle.