Figure 1.

(a) A diagram depicting the phosphorylation and sequestration of a substrate B. B_i (i = 0, 1, 2,…, n) represents free substrate B that has been phosphorylated on a total of i sites, S represents the sequestering entity (e.g., membrane surface, nucleus, or a binding protein), and B_iS represents the sequestered phosphoforms of B. The values k_i and d_i are rates for the phosphorylation and dephosphorylation reactions, respectively. Rate coefficients $k_{\mathrm{i}}^{\mathrm{a}}$ and $k_{\mathrm{i}}^{\mathrm{d}}$ characterize binding to and dissociation from S. (b) The corresponding reaction diagram. A represents the kinase; the phosphatase is not explicitly shown.