The invention relates to a method for determining the ability of a molecule to modulate the activation of a
G protein-coupled
receptor (GPCR), said method comprising the following steps:a) introducing, in a first container:a membrane preparation bearing one or more GPCRs and one or more alpha G-proteins,a source of nonhydrolyzable or slowly hydrolyzable GTP labeled with a first member of a pair of RET partners,a ligand of the alpha
subunit of a
G protein (alpha G-
protein) labeled with a second member of the pair of RET partners, said ligand being capable of binding to the full alpha G-
protein bound to the nonhydrolyzable or slowly hydrolyzable GTP labeled with the first member of a pair of RET partners,optionally a GPCR
agonist;b) measuring the RET
signal emitted in the first container;c) introducing (i) in a second container, the same reagents as in step a) and the molecule to be assayed or (ii) in the first container, the molecule to be assayed;d) measuring the RET
signal emitted in the second container or in the first container obtained in step c);e) comparing the signals obtained in steps b) and d), a modulation of the
signal obtained in step d) relative to that obtained in step b) indicating that the molecule to be tested is capable of modulating the activation of the GPCR.