This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Action of the alpha subunit of G-protein is: \nSelect and explain. \nA. Binding of antagonist, B. Breakdown of GTP to GDP, C. Conversion of GDP to GTP, D. All of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.\nKEY CONCEPT:-\nAlpha subunit of G protein contains GTPase which breaks GTP into GDP.\nReference: Essentials of Medical Pharmacology Eighth Edition KD\xa0TRIPATHI\xa0page no 55', 'role': 'assistant'}]