CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE FROM A PARTICULATE FRACTION OF RAT-HEART - SOLUBILIZATION AND CHARACTERIZATION OF A SINGLE ENZYMATIC FORM

Approximately 2-8% of the cyclic nucleotide phosphodiesterase (PDE) activity of a crude 1000 g supernatant from rat heart was associated with the washed 105,000 g pellet fraction. This activity exhibited biphasic Lineweaver-Burk plots over a large range of cyclic nucleotide concentrations. Concave-downward plots were obtained with cAMP as the assay substrate, while cGMP gave rise to concave-upward plots. Treatment of this particulate fraction by freezing and thawing and then with 2% Lubrol PX released the major part of PDE activity into the supernatant (70 and 90% for cAMP and cGMP phosphodiesterase activities, respectively). Isoelectric focusing of the solubilized enzyme revealed a single peak of PDE activity. While the Lineweaver-Burk plots of cAMP PDE activity were not markedly modified by detergent treatment, kinetic plots of cGMP PDE activity underwent a drastic transformation during the overall solubilization procedure. The substantial increase in the cGMP rate of hydrolysis observed at low substrate level might explain the difference in the apparent yield of solubilization between cAMP and cGMP PDE activities.