A simple fluorimetric assay for guanosine nucleotides

It is comparatively easy to assay adenosine 5′-triphosphate either in the presence or absence of other nucleoside triphosphates (1). An assay for UTP has been reported (2) based on its incorporation into RNA using RNA polymerase and a poly(dA-dT) template in the presence of excess [³H]-ATP; this method could be adapted to assay for GTP and CTP. It is known that the fluorescence of Tb³⁺ increases on binding to nucleic acids (3–5), and this enhancement has been attributed both to complex formation between Tb³⁺ and guanine residues in the nucleic acid (3) and also to binding of Tb³⁺ to thiouracil (4).