Increased phosphorylation in vitro of a cytosolic polypeptide resolved from denervated skeletal muscle

The in vitro phosphorylation of a 40,400-dalton, cytosolic polypeptide from the soleus muscle of the rat is increased twofold within 24 hr after cutting the motor nerve fibers to this muscle. This involves an ATP-phosphotransferase reaction which we have reported to be inhibited by a specific cyclic AMP-dependent protein kinase inhibitor. The phosphorylated polypeptide does not electrophoretically comigrate on SDS-polyacrylamide gels with the 38,000-dalton catalytic subunit of cyclic AMP-dependent protein kinase which is known to undergo a site-specific autophosphorylation in skeletal muscle.