Regulation of cyclic adenosine 3':5'-monophosphate phosphodiesterases. Interrelationship of the various forms in rat skeletal myoblasts and adult muscle.

5Cl In rat skeletal myoblasts and adult muscle extracts, four forms of a high affinity cAMP phosphodiesterase are found in vitro.These are termed PDE 1, PDE 11, PDE 111, and PDE IV, and have approximate molecular weights of 1.5 X lo6, 400,000, 120,000 and 60,000, respectively.Evidence is presented to show that there is only one primary form of phosphodiesterase in myoblasts, uiz PDE 11, with the rest of the forms being derived from it.When partially purified PDE II is treated with ammonium sulfate, a-tocopherylphosphate, or stored at 4 "C, or chromatographed on a methylisobutylxanthine-Sepharose column, it is converted into PDE I, thus suggesting that PDE I is an aggregated form of PDE 11.PDE I consists of only one type of subunit with a molecular weight of about 94,000.PDE I1 thus is a tetramer.Partially purified PDE 11 and PDE 111, when treated with various proteases, yield a form which is identical with a homogeneously purified preparation of PDE IV.The latter has two subunits of molecular weight 28,000 and 30,000, both of which have aspartate as the NHz-terminal amino acid, and probably arise from PDE 11 by proteolytic cleavage.Since PDE I1 and PDE I11 both give rise to PDE IV upon proteolysis, it is possible that PDE I11 also arises from PDE 11.Out of the four forms of phosphodiesterase, PDE I and PDE IV are probably artifacts of homogenization.Formation of PDE III, however, may have regulatory significance.The apparent K,,, values of all forms of phosphodiesterases are about 2 CM, but they differ in their sensitivity to activation by proteases and some other compounds.Only PDE II is activated by proteases, NaSCN, and a-tocopherylphosphate.The presence of multiple forms of cAMP phosphodiesterases in mammalian tissues has been well documented (review in Ref. 1).These forms include those which have low affinity for cAMP and are activated by calmodulin, those with high affinity for cAMP and unaffected by calmoddin, as well as forms capable of hydrolyzing both cAMP and cGMP as substrates.Recently, calmodulin-activated phosphodiesterase has been purified to homogeneity from bovine brain (2-4) and bovine heart (5).So far, there has been only one report of purification of a high affinity phosphodiesterase, that from