Methods

For modeling the cascade, we used standard reaction schemes. Complex-binding is described by bimolecular reactions

$$A+B \begin{array}{c} k_f \\ [-3mm] \rightharpoonup \\ [-3mm] \leftharpoondown \\ [-3mm] k_b \end{array}$$ (1)

and for enzyme catalyzed reactions we apply the standard Michaelis-Menten formulation with the assumption of an irreversible final step:

$$S + E \begin{array}{c} {\scriptstyle k_1} \\ [-3mm] \rightha... ...tyle k_3} \end{array} SE \stackrel{k_2}{\rightharpoonup} P + E$$ (2)

From this reaction equations first order ordinary differential equations were derived and integrated using fourth order Runge-Kutta integrator with stepsize-control written in C[10]. For finding steady states we integrated the system until the relative change of all concentrations per time went under a certain limit. All calculations were performed on a Linux workstation.