Epididymal Sperm cAMP-Dependent and cAMP-Independent Protein Kinase Activity and Phosphorylation in the Rat

Rat caput and cauda epididymal sperm cAMP-dependent and cAMP-independent protein kinase activity was determined in three buffers with and without calcium. In all buffers, higher enzymatic activity for both enzymes was found in cauda than in caput sperm. Maximum protein kinase activities were found in a sucrose-magnesium phosphate buffer. A Krebs Ringer phosphate buffer distinguished cAMP-dependent and cAMP-independent activity in cauda but not caput sperm. Sucrose-TRIS buffer was shown to be of little value for measuring enzyme activity in either cell type. When protein phosphorylation was examined with 0.5 mM calcium and 2.5 mM cAMP, inhibition of both caput and cauda sperm phosphorylation occurred. When cAMP concentration was lowered to microM, or nM, or pM levels, cAMP-dependent protein phosphorylation was restored.