Figure 4. Time courses of active transducin (T*) and phosphodiesterase (PDE*) determined with a stochastic simulation. A: Two independent repetitive cycles of reactions show the time course of accumulated concentrations of Tαβγ-GTP and PDE* after the activation of single rhodopsin. B: The whole cycle is repeated 10,000 times to get the result summed over many quanta. Time constants (in ms) are t₀ = 1, t₁ = 4.7, t₂ = 0.1, t₃ = 0.1, t₄ = 0.1. Total duration of the activation cycle (t₁ + t₂ + t₃ + t₄ = 5 ms) was fixed according to biochemical data on the rate of T activation in frog rods (about 200 s⁻¹ [19]). t₅ = 2.5; t₆ = 2.5. t₀ is the time of Meta II production in frog rods [17].