<prompt> Action of the alpha subunit of G-protein is:Binding of antagonistBreakdown of GTP to GDPConversion of GDP to GTPAll of the above  <response>: The α-subunit has GTPase activity: the bound GTP is slowly hydrolysed to GDP: the α-subunit then dissociates from the effector to rejoin its other subunits, but not before the effector has been activated inhibited for several seconds much longer than the life-time of the activated receptor, which is in milliseconds and the signal has been greatly amplified. The rate of GTP hydrolysis by the α subunit and thus the period for which it remains activated is regulated by another protein called regulator of G protein signaling RGS. The onset time of response through GPCRs is in seconds.KEY CONCEPT:-Alpha subunit of G protein contains GTPase which breaks GTP into GDP.Reference: Essentials of Medical Pharmacology Eighth Edition KD TRIPATHI page no 55 