An easy and rapid method for the measurement of [γ-P]ATP specific radioactivity in tissue extracts obtained from in vitro rat heart preparations labeled with Pi

A rapid method for the measurement of γ-³²P]ATP specific radioactivity in tissue extracts containing other ³²P-labeled compounds is described. The neutralized acid extract is incubated with cyclic AMP-dependent protein kinase, cyclic AMP and casein. The incorporation of ³²P into casein from γ-³²P]ATP is measured by perchloric acid precipitation of the protein on filter paper. ³²P-Casein formation is linearly related to the specific radioactivity of the γ-³²P]ATP. Separation of ATP from other ³²P-labeled compounds is not required for the assay. Application of this method in the evaluation of γ-³²P]ATP specific radioactivity in two rat cardiac muscle preparations exposed to ³²P_i is demonstrated.