Fig 4. Depth γ of the nanocompartments formed by a single PDE molecule as a function of the cAMP concentration c for different values of absorptive action η.

The concentration c is given in multiples of the Michaelis-Menten constant of the PDE $c=\frac{\rho }{K_m}$, the absorptive action η is defined as $\eta =\frac{k_{cat}}{4\pi R_{\text{PDE}}D{K}_m}$. The deepest compartments are found in the limit c → 0, where $\gamma =\frac{1}{1+\eta }$. When the cAMP concentration is increased (c → ∞), the compartments get flooded and disappear due to saturation of the PDE. Dots indicate the concentration at which the compartment is half way flooded and are found at $c_{1/2}=\frac{{(1+\eta )}^2}{1+\eta /2}$.