Molecular heterogeneity of rabbit heart phosphorylase kinase

Phosphorylase kinase (ATP: phosphorylase-b phosphotransferase, EC 2.7.1.38) from rabbit heart, when submitted to electrophoresis on Pevikon, separates into two discrete peaks A and B. The two peaks have been analyzed using reelectrophoresis, chromatography on DEAE-cellulose, thermal stability, inactivation by EGTA (ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) and reaction with an anti-muscle phosphorylase kinase antiserum. It can be concluded that rabbit heart extracts contain two isozymes of phosphorylase kinase. The more negatively charged isozyme seems to be identical with the muscle enzyme. The other isozyme resembles the liver enzyme but differs from the major fraction of the latter by its charge. It is likely that there exist at least three molecular types of phosphorylase kinase.