Reconsideration of the multiple cyclic nucleotide phosphodiesterases in bovine heart.

DEAE-cellulose chromatography demonstrated the presence of three peaks of cyclic nucleotide phosphodiesterase activity in the hearts of cattle during the summer and only two peaks during exposure to freezing temperatures. The hydrolysis of 10^?6M cyclic AMP by peak II, the variable activity, was stimulated 160% by 10^?6M cyclic GMP and was inhibited by chelation of Ca²⁺. Peak II activity was not a distinct enzyme but rather a mixture of activator-dependent phosphodiesterase, phosphodiesterase activator and type II cyclic AMP-dependent protein kinase.