Figure 1. Determining kinetic parameters for MEK activation of ERK.

A) Kinetics of ERK phosphorylation by active wild type MEK. The three different ERK phosphostates were quantified via phostag gels. S₀, S₁, S₂ represent unphosphorylated, monophosphorylated, and dually phosphorylated ERK respectively. B) Model fit to the kinetic data. The error bars indicate the standard deviation of the 12 replicates. The lines show a fit to the reduced model (Figure 2A) obtained using Bayesian inference. C) General model describing the mechanism by which a kinase phosphorylates a substrate with two ordered phosphorylation sites.