Enzyme Localization Can Drastically Affect Signal Amplification in Signal Transduction Pathways
Figure 3
Effect of the Diffusion Coefficient on the Response
The input–output relation of a network in which the activating enzyme is located at one pole, while the other components can freely diffuse in the cytoplasm, is plotted for different values of the diffusion constant D (in μm2s−1) of the cytoplasmic components. The inset shows the logarithmic gain g ≡ ∂ln[X*]T / ∂ln[Ea]T. It is seen that the gain of the push–pull network strongly increases with increasing diffusion constant. If D → ∞, the dose–response curve approaches that of the push–pull network in which the components are uniformly distributed in space (and that of the network in which the enzymes are colocalized). The total substrate concentration is [S]T = 20 μM, the total concentration of the deactivating enzyme is [Ed]T = 0.5 μM, the Michaelis-Menten constants are KM,a = KM,d = 0.5 μM, and the catalytic rate constants are k3 = k6 = 25s−1.