distinguishing between agonist and antagonists - Radioligand receptor binding (Jun/03/2008 )

Hi there,

Is it it possible to tell the difference between an agonist and antagonist in a radioligand binding assay...ive come ax heaps of sites saying no you can't so that is what i wrote in my lab report...howeeeeeva...when i got my mark back one of the comments was "if the receptor is a g-protein coupled receptor, do you think that the addition of GTPgammaS means that we can distinguish an agonist from an antagonist? YES!"

sooo im thinking what does this exactly mean??

GTP is for (heterotrimeric) GTPase on the effector site of G-coupled receptors; G-protein-coupled receptor will be activated by agonists, and not by antagonists; so, GTPase cleavage will be a functional assay for receptor activation...