Determination of soluble CAMP-dependent protein kinase activity in guinea-pig tracheal smooth muscle Preferential use of kemptide as a phosphorylating substrate

A method is described for the determination of soluble (cytosolic) cyclic AMP (cAMP)-dependent protein kinase (A-kinase) activity in guinea-pig tracheal smooth muscle. The method relies upon the use of either histone or kemptide as a phosphorylating substrate. The relative merits of each of these substances were compared by studying the effects of a protein kinase inhibitor (PKI) and of Na+ on the phosphorylation of each substrate. PKI induced …