Abstract: The present invention provides fluorescent cyanine dye-based nucleotide analogues, in which the cyanine dye is coupled to the ?-phosphate group of a nucleoside triphosphate. Preferred embodiments of the invention are directed to fluorescent cyanine dye-based GTP analogues which may be employed in an homogeneous FRET-based assay to measure the binding of guanine nucleotides to GPCR polypeptides, or alternatively, to measure the effect of an exogenous ligand on GPCR protein binding.

Abstract: The invention provides a method for measuring binding of a test compound to a G-Protein Coupled Receptor (GPCR). The invention also provides a method for identifying and measuring the effect that an agent has upon modulating the binding of a test compound to a G-Protein Coupled Receptor.

Abstract: Various classes of dyes are provided having acid, ester or amide groups for covalent linking to biomolecules. The dyes may be prepared by use of a compound of formula (I) where R1 comprises a linker and a carboxy including acid, salt, ester including N-hydroxysuccinimide, activated ester or amide group; R2, R3, R4 and R5 are H, C1-C10 alkyl or aralkyl or a group to modify solubility or electronic or spectral properties or a functional linking group: or R4-R5 and/or R2-R4 and/or R2-R3 are linked to form an extended ring system; and R6 is H or CHO or NO.