Fig 6. The dynamics of protein phosphorylation.

A. Given a protein Y, the accumulation of its phosphorylated form, Y^P, is determined by the activity rates of its kinase and phosphatase (k and p, respectively). B. The level of Y^P as a function of time (t). Y^P starts at zero and ends at its steady state level, described by the equation: Y^P(t) = k/p * (1−e^−pt). The black line depicts the regular activity rates (k = 1, p = 1, denoted KK and PP, respectively). The blue line depicts a 2-fold increase in the steady-state level of Y^P, achieved by doubling the kinase activity (k = 2 and p = 1, denoted as KKKK and PP, respectively). The response time t_1/2 (dashed black line) is identical in both cases. C. The black line is as described in B. The red line depicts a 2-fold increase in the steady-state level of Y^P, achieved by 2-fold decrease in the phosphatase activity (k = 1, p = 0.5, denoted as KK and P, respectively). The response time t_1/2 in this case (dashed red line) is twice the response time of the regular case.