DIRECT PHOTO-AFFINITY LABELING WITH CYCLIC NUCLEOTIDES: ACTION SPECTRA

Abstract— When ³H]-cyclic adenosine 3',5'-monophosphate and ³H]-cyclic guanosine 3',5'-monophos-phate are irradiated at varying UV wavelengths in the presence of cyclic nucleotide receptor proteins, photo-incorporation is maximal in the region of 280 nm. This suggests that covalent coupling occurs by means of photo-activation of an entity other than the ligand cyclic nucleotide. The action spectra more closely resemble the absorbtion spectrum of the reacting protein, making it likely that absorhtion of radiant energy by components of the protein receptor leads to photo-affinity labeling.