Investigations on adenosine 3', 5'-monophosphate phosphodiesterase in ram semen and initial characterization of a sperm-specific isoenzyme

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Abstract
Phosphodiesterase occurs in ram semen, and its activity is higher in spermatozoa than in seminal plasma. Using similar substrate levels, the rate at which c[cyclic]AMP is metabolized by phosphodiesterase in spermatozoa is about 100 times higher than that of cAMP synthesis by adenylate cyclase. In spermatozoa phosphodiesterase is present partly in a soluble form, and partly bound; both forms can be extracted by sonication. The soluble enzyme (pH optimum 8.0, Km = 1.5 .mu.M, MW 165,000) occurs as a single isoenzyme, as shown by polyacrylamide gel electrophoresis and anion-exchange chromatography; this isoenzyme appears to be specific for spermatozoa, and its formation in the testis coincides with the appearance of spermatozoa. The bound sperm enzyme was solubilized with Triton X-100; it is a single isoenzyme (pH optimum 8.0, MW 165,000) which is electrophoretically different from the soluble form, but similar to the phosphodiesterase found in other tissues. Seminal plasma phosphodiesterase (pH optimum 8.8, MW 165,000) is present in the form of 3 isoenzymes; all 3 are different from the 2 forms of sperm phosphodiesterase, but are similar to the isoenzymes found in certain male accessory organs.