Behavior of PLC and CaPLCcomplex, realizations and estimated PSDs. (A) Realizations for PLC. (B) Realizations for CaPLCcomplex. The realizations are simulated using the Gillespie SSA in four different system volumes, 5 × 10-16 l (blue), 3.5 × 10-15 l (red), 10-14 l (green), and 10-13 l (black). The discrete nature of reactions can be easily seen in the smallest volume. In larger volumes, the strength of noise is smaller but still detectable. (C) Frequency domain behavior for PLC. (D) Frequency domain behavior for CaPLCcomplex. The estimated PSDs for PLC and CaPLCcomplex in different volumes (5 × 10-16 - 10-13 l) are illustrated by representing the frequency content of signals by color coding (heat map). The PSDs were estimated using 10 second signals (simulated noise processes). The noise in both species has more power on lower frequencies than higher frequencies.