A simple assay method for determination of the specific radioactivity of the γ-phosphate group of 32P-labelled ATP.

Abstract
A simple and rapid assay method is described for determining the specific radioactivity of the .gamma.-phosphate group of 32P-labeled ATP. Labeled ATP is incubated with cAMP, [bovine heart] cAMP-dependent protein kinase and histone H2A under conditions leading to maximum phosphorylation of the histone. The specific radioactivity of the .gamma.-phosphate group of the 32P-labeled ATP is calculated from the total amount of [32P]Pi incorporated into a standard amount of histone. This assay amount uses inexpensive commerically available materials, and it yields an accurate specific radioactivity with as little as 0.25 nmol of 32P-labeled ATP.