Figure 7.

Dynamical behavior of the final model with Cdh1 as an S substrate. (A) Schematic diagram. (B) Time courses of Cdk/cyclin, S (Cdh1), S_PP (Cdh1_PP), APC_PP, securin, and cell mass. Notice that Cdh1 allows an extended G1 phase where S is unphosphorylated (compare Fig. 7B with Fig. 6B). In this case, terms for Cdk degradation by Cdh1, $k_{dcdk2}\times Cdk\times S$, and for securin degradation by Cdh1, $k_{dsec2}\times Sec\times S$, are added to Eqs. 7 and 9, respectively. (C–E) Bifurcation diagrams of Cdk/cyclin, S_PP, and APC_PP are plotted as functions of cell mass, considered as a parameter. Superimposed on these bifurcation diagrams are the limit-cycle oscillations (closed curve) in B. Parameter values for the simulations are given in section 5 of Supplement 1 in the Supporting Material.