Figure 8

Layer based modularization of the larger example system. In the larger example system the left module describes the receptor layer. The output of this layer is the sum of all species which are phosphorylated on the binding site for E. This sum is denoted as x. The upper right module, which describes the layer of effector E, returns the sum of occupied binding sites (xb) and sends the sum of all species which are phosphorylated on the binding site for F (x 2). The lower right module, which describes the layer of effector F, returns the sum of occupied binding sites x 2b. The sum of catalytically active receptors is denoted as R _activ . All reactions are reversible, arrows definne directions of positive rates. For equations see Additional file 4.