Abstract: The invention relates to antibodies or antibody fragments capable of binding to G-protein alpha, nucleic acid sequences coding for the antibody, vectors comprising the nucleic acid sequence, cells comprising the vector or the nucleic acid sequence and a kit-of-parts comprising (i) the antibody or antibody fragment or the composition and (ii) a source of GTP labeled with a member of a pair of RET partners.

Abstract: The invention relates to compounds of formula: in which X, Y, L and Ln3+ are as defined in the description.

Abstract: 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