Catalytic subunit of cAMP-dependent protein kinase from bovine heart: several isoforms demonstrated by high resolution focusing in immobilized pH gradient.

The catalytic subunit (C) of cAMP-dependent protein kinase holoenzyme type II from bovine cardiac muscle was separated by isoelectric focusing in Immobiline polyacrylamide gels into 9 protein forms. The major forms (i) appeared at pH 7.1, 7.4, 7.5, and 7.7, (ii) exhibited protein kinase activity and were inhibited by heat and acid stable inhibitor, (iii) represented approx. 30%, 4%, 64%, and 1% of the protein respectively, (iv) refocused in the same position from which they had been eluted from the first gel. Antibodies against C detected additional proteins at approx. pH 7.55, 7.75, and 7.8. Two more bands became detectable at approx. pH 7.3 and 7.45 by application of antibody against C beta (Uhler, M.D. & McKnight G.S. 1987, J.Biol.Chem. 262, 15202-15207). The relation of the different forms of C to the fractions CA and CB (Kinzel V. et al. 1987 Arch. Biochem. Biophys. 253, 341-349) is demonstrated.