Figure 2.

A schematic representation of the activation model given by equation (2). Two monomers interact laterally to form dimers, both in the absence and presence of bound ligand (dimerization constants K₁ and K₂, respectively). The ligand binds to both monomers (association constant K_M) and dimers (association constant K_D). The receptors in the unliganded and liganded dimeric states are phosphorylated, but the probabilities for phosphorylation may be different (Φ_d for the unliganded state and Φ_D for the liganded state).