Figure 7.

Dynamics of Cdk1 Substrate Specificity during the Cell Cycle

(A) A schematic view of the dynamic changes of Cdk1 specificity during the cell cycle.

(B) Modified Michaelis-Menten formula with the highlighted inhibitory term describing how the Cdk1 substrate pool (S_TOT) can act as a competitive inhibitor relative to any particular substrate (S_X). The lower panel on the left side presents a schematic view of a hypothetical system based on sequential accumulation of three cyclins with gradually changing specificity, and the panel on the right side presents a similar system with a single mitotic cyclin (rising linear lines). The gradual phosphorylation and decrease of the unphosphorylated Cdk1 substrate pool during the progression of the cell cycle is depicted as the declining black line. In the three-cyclin system, the inhibitory terms (1 + S_TOT/K_M,TOT) are kept relatively low and equal throughout the course of the cyclin synthesis, because as the substrate pool gets gradually phosphorylated S_TOT for each cyclin decreases in correlation with K_M,TOT. In the system with a single cyclin, the inhibitory term is high in the early stages of the cell cycle, potentially delaying timely phosphorylation of premitotic targets.