Assay and purification of calmodulin-dependent protein kinase

Posttranslational modification has long been recognized as a way in which the properties of proteins may be subtly altered after synthesis of the polypeptide chain is complete. Amongst the moieties most commonly encountered covalently attached to proteins are oligosaccharides, phosphate, acetyl, formyl, and nucleosides. Posttranslational covalent modification of protein by phosphorylation is one of the most prevalent and best understood mechanisms employed in cellular regulation (1-9). Protein kinases catalyze the transfer of the γ-phosphoryl group of adenosine triphosphate (ATP) to an acceptor protein substrate. The activity of the enzyme is determined by the transfer of (32)P (labeled γ-phosphate) from [γ-(32)P] ATP to protein substrate.