A Radioimmunoassay for cyclic AMP (cAMP) Obtained by Acetylation of Both Unlabeled and Labeled (3H‐cAMP) Ligand, or of Unlabeled Ligand only

Abstract
A sensitive radioimmunoassay (limit of detection 7 .+-. 1 fmol per tube) for cyclic[c]AMP based on acetylation of both 3H-cAMP and unlabeled ligand was developed. Rabbit anti-cAMP antibodies had an apparent Ka for the acetylated ligand of 2 .times. 1010 l/mol. When the unlabeled ligand only was acetylated, an increased sensitivity was obtained without loss of specificity.