Figure 15

Special case: One molecule can bind on different sites on another molecule. In (a) the cartoon of the example system is depicted. Molecule A can bind on two different sites on a molecule R; both sites have to be phosphorylated previous to the binding. (b) Process node 1 and 2 represent modification processes, process node 3 and 4 the two binding processes. Each modification process on the particular site exerts an influence in form of an all-or-none interaction on the following binding process. In (c) one L-node is introduced for each site of a molecule (R_p1, R_p2 and A_b1). Additional L-nodes representing the basal activity of molecule A and R have an activating influence on L-nodes representing the sites. The arrows from R_p1 to A_b1 and from R_p2 to A_b1 represent the two all-or-none interactions among modification and binding processes. In this logical model the two binding processes are represented by a single L-node. As described above, every P-node has to correspond to a unique L-node. Hence, a further L-node has been introduced in the logical model shown in (d) to enable a one-to-one correspondence of P-nodes to L-nodes.