Time course of the inactivation of cAS-PDE by 8-BDB-TcAMP. (A) The enzyme was incubated at 25°C with the 8-BDB-TcAMP (○, 0.3; □, 0.6; ▵, 1.2; ▿, 2.5; •, 4; and ▪, 8 mmol/L) in 50 mmol/L HEPES buffer, pH 7.5, 20% glycerol and 5 mmol/L MgCl₂ . Aliquots (2 μL) were removed, diluted 1,000-fold, and the diluted solution was assayed in triplicate. The results were corrected for the control which retained >95% of starting activity over the course of the experiment. (B) The pseudo-first-order constants k′ were plotted against the concentration of 8-BDB-TcAMP to obtain the second-order rate constant (0.022 min⁻¹mmol/L⁻¹).