Calmodulin regulation of testicular cyclic nucleotide phosphodiesterases.

Three different, calmodulin-dependent, isoenzymes of cyclic nucleotide phosphodiesterase (PDE) can be isolated by DEAE cellulose chromatography from the immature rat testis and shown to have different substrate specificities and kinetic behaviour. Calmodulin is regulating the activity of these enzymes by altering the maximal velocity (Vmax) rather than the Km of the reaction. Two of the 3 enzymes appear to be testis-specific, while the remaining possesses properties similar to that described for the calmodulin-dependent PDE found in other tissue.