Steady-state response curves without the external feedback loops.

<p>GF (growth factor) is the bifurcation parameter that is being changed. Red and blue curves are the stable and unstable branches, respectively. LP: Limit Point bifurcation also called the turning point at which the switch between the low and high stable branches occurs. (A) Since bistability curve is so flat for the <b><i>SOS</i></b>_{<b><i>complex</i></b>}, the unstable blue branch is squeezed between the two red stable branches and is not visible. (B) <i>RasGTP</i> response. The switch between the low and high stable branches occurs at the turning points, and it is shown by the arrows. (C) Ultrasensitive <b><i>MEK</i></b>^{<b><i>PP</i></b>} response. (D) Bistability is sustained in <b><i>ERK</i></b>^{<b><i>PP</i></b>} response.