Fig 3. T-cell antigen receptor ultrasensitivity from Beacon Calculus simulations.

(a) An enzyme enters the proximity of a receptor, binds to the receptor, and phosphorylates the receptor if the enzyme is a kinase or dephosphorylates the receptor if the enzyme is a phosphatase. (b) T-cell antigen receptor model written in the Beacon Calculus with parameters taken from [36]. (c) The fraction of phosphorylated receptors is ultrasensitive to the relative concentration of kinase and phosphatase when the enzyme dwells after modifying a receptor (green) but loses ultrasensitivity if the dwell is removed (blue). Points (shown with standard deviation) are the average of 50 simulations taken after the system reaches a steady state.