Testicular cyclic nucleotide phosphodiesterase in the rat. Kinetic properties and changes with age

The assay for cyclic nucleotide phosphodiesterase has been applied, with certain modifications, to the measurement of the soluble forms of these enzymes in the rat testis. The homogenization and incubation conditions were adjusted to achieve linear product formation as a function of time and protein concentrations and the resulting products were isolated by ion exchange chromatography using 5 mM HCl as the eluting agent. Phosphodiesterase activities were present in the testicular cytosol (105,000 g supernatant) of adult rats which were capable of hydrolyzing cAMP with a high (Km2 microM) and low Km20 microM) affinity and GMP with a relatively high affinity (Km3 microM). The low affinity cAMP enzyme activity could be stimulated with divalent ions such as calcium, magnesium, and manganese. At 18 days of age, all three enzyme activities were present in the testis, although both the high and low affinity cAMP phosphodiesterase displayed maximal rates (Vmax) that were only one third of the adult testis (when expressed per mg protein).