Caliper Mobility-Shift Assay: To a 96-well plate, 20 μL, of 10 μM FL-cGMP as the substrate was added; then 1 μL, of solution of the compound in DMSO or DMSO solution without compound was added, and then 29 μL of 1.38 ng/μL PDE-5A enzyme buffer (100 mM Hepes pH 7.5, 5 mM MgCl2, 0.002% Brij-35) was added. The maximum final concentration of the compound was 10 μM. The plate was incubated at 30° C. for 1 h, and 20 μL of 70 μM EDTA was then added to stop the reaction. 26 μL of solution of each well was transferred to a 384-well plate.
Enzyme Assay: The test compound or solvent was incubated at 25° C. for 15 min with enzyme solution (35 μg/mL) in Tris-HCl buffer of pH 7.5. 1 μM cGMP and 0.01 μM [3H] cGMP were then added to activate the reaction. The mixture was incubated for 20 min. The reaction was stopped at 100° C. By addition of snake venom nucleotidase, the product [3H] GMP was converted into [3H] Guanosine, which was separated with AG1-X2 resin. Then the amount of [3H] Guanosine was measured.
Enzyme Assay: Method: The test compound or solvent was incubated at 25° C. for 15 min with enzyme solution (0.2 μg/mL) in Tris-HCl buffer of pH 7.5. 100 μM cGMP and 0.03 μM [3H] cGMP were then added to activate the reaction. The mixture was incubated for 20 min. The reaction was stopped at 100° C. By addition of snake venom nucleotidase, the product [3H] GMP was converted into [3H] Guanosine, which was separated with AG1-X2 resin. The amount of [3H] Guanosine was measured.