Figure 2. Time course of the production of active transducin (T*) and phosphodiesterase (PDE*) (modified from [1-3]). Times from t₀ to t₆ represent the durations of corresponding transitions in Figure 1 (state 0 to state 1, state 1 to state 2, etc.). The straight line initiating from t₄ shows the time course of T* production, at the rate of ν_RG. The first PDE* would ideally appear at t₆. The bent red line shows a more realistic approximation that may result from the extra delay between T*–PDE binding and activation of PDE. ν_RE is the steady rate of PDE* production achieved after an effective delay t_eff. In accordance with [3], we further assume ν_RE = ν_RG. t_d > t₆ is placed, rather arbitrarily, as the delay time when the minimum deviation of PDE* from its dark level can be detected.