Fig. 4.

Total protein gradients in the bacterial chemotaxis signaling pathway. (a) Schematic of the relevant reactions modeled. CheY (Y) is phosphorylated by the kinase CheA (A). Up to two CheY-phosphates (Yp) can bind sequentially and reversibly to the dimeric phosphatase CheZ (Z₂). Upon hydrolysis, unphosphorylated CheY is released. The phosphorylation reaction at CheA consists of several reactions. For details and all rate constants, see Table 1. (b) Snapshot of a Smoldyn simulation at steady state; diffusion coefficients as in (d). On the left is a fixed array of CheA kinases, all other molecules are diffusing freely. Colors as in (a). Monomers and dimers are shown as small spheres, all larger complexes as large spheres. (c–f) Results of stochastic simulations with Smoldyn. Means of 1000 timepoints.