A Protein Binding Assay for Adenosine 3′:5′-Cyclic Monophosphate

A simple and sensitive assay for adenosine 3′:5′-cyclic monophosphate (cAMP) has been developed that is based on competition for protein binding of the nucleotide, presumably to a cAMP-dependent protein kinase. The nucleotide-protein complex is adsorbed on a cellulose ester filter. Assay conditions are such that a binding constant approaching 10 ^-9 M is obtained, and the assay is thus sensitive to 0.05-0.10 pmol of cAMP.