Radioimmunoassay of bovine heart protein kinase

Immunization of guinea pigs with bovine cardiac cAMP dependent protein kinase (ATP protein phosphotransferase, EC 2.7.1.37) resulted in the development of precipitating antibodies to the cAMP binding subunit of the enzyme. Both the phosphorylated and nonphosphorylated cAMP binding protein of the protein kinase reacted with the antiserum. A radioimmunoassay was developed that detects 10 ng of holoenzyme and permits measurement of enzyme concentrations in bovine cardiac muscle. Bovine liver, kidney, brain, and skeletal muscle contain protein kinases which are immunologically identical to those found in bovine cardiac muscle. However, the proportion of immunoreactive enzyme activity differed for each tissue. All of the immunologically nonreactive enzyme in skeletal muscle and heart was separable from immunoreactive enzyme by chromatography on DEAE cellulose. Rat tissues and pig heart contained protein kinase activity that crossreacted immunologically in a nonparallel fashion with bovine cardiac enzyme. These results indicate that cAMP dependent protein kinases within and between species are immunologically heterogeneous.