BODIPY FL adenosine 5'-triphosphate and BODIPY FL guanosine 5'-triphosphate (G-12411) are composed of a BODIPY FL fluorophore attached to the 2' or 3' position of the ribose ring via a linker. Interactions between the fluorophore and the purine base are evident from the spectroscopic properties of these nucleotide analogs. The fluorescence quantum yield of BODIPY FL GTP is only about one-tenth that of BODIPY FL ATP; however, this yield may be enhanced upon binding of BODIPY FL GTP to GTP-binding proteins.