Characterization of PDE activity and inhibitor potency. Panel A: Michaelis-Menten kinetics of recombinant LmjPDEB2 with 3H-cAMP as substrate. Panel B: reaction in the presence of a 100-fold excess of unlabelled cGMP. Panel C: reaction in the presence of a 50-fold excess of unlabelled AMP. Inserts in A – C: corresponding Eadie-Hofstee plots. Panel D: Effect of PDE inhibitors on LmjPDEB2 activity (1 μM 3H-cAMP substrate, 100 μM inhibitor). 1, cilostamide; 2, zaprinast; 3, etazolate; 4, dipyridamole; 5, Ro-20-1724; 6, rolipram; 7, IBMX; 8, 8-methoxy-methyl-IBMX; 9, trequinsin; 10, papaverine; 11, milrinone; 12, pentoxifylline; 13, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA). Very similar results were obtained with LmjPDEB1.