Competitive Protein Binding Assay of Camp1Using Thyroid Cytosol

Abstract
We describe here a competitive protein-binding assay (CPBA) of cAMP which employs a crude thyroid cytosol preparation as the ligand-binding reagent. The affinity constant (Ka) of the binding of cAMP to the thyroid receptor varied between 1 and 4 × 109 M−1 in the assay. ATP, ADP and AMP did not interfere in the assay. Cross -reaction of cGMP, 1.8%, and that of cIMP, 36%, were comparable to those observed with previously described CPBAs of cAMP. The range of the assay standard curve was 0.5—20.0 pmoles per tube. Coefficient of variation was 8.3% within an assay and 8.7% between assays. The assay was applied to measurement of cAMP in biologic fluids and tissues. The results were comparable to those obtained with previous methods.