Turnover number and inactivation kinetics of GC. (A) Time course of cGMP production in the presence of 1 mM IBMX at different resact concentrations. Error bars are means ± SD from at least three experiments. (B) Time course of cGMP synthesis (red triangles) for sperm stimulated with 250 nM resact. The apparent turnover number of GC (black squares) was calculated by using Eqs. 1–3 (Materials and methods). The data shown are from a single representative experiment out of 12 from six different animals. Lines represent exponential fits. (C and D) Turnover number (C) and inactivation rate of GC (D) versus resact concentration. Each data point represents the mean ± SD. Dashed lines denote the mean turnover number and inactivation rate over all concentrations, respectively (T = 72.2 ± 28.7 cGMP molecules/second; ki = 6.4 ± 2.4 s−1). Number of experiments is given in parentheses above the data points. Turnover numbers and inactivation rates were calculated from time courses of cGMP.
