Kinetic model for the activation of EMTr and EMTm. The model assumes two binding sites for inhibitor (I) or radiolabeled substrate (S) per transporter entity (E). For a full mathematical description of complex formation and substrate turnover, 10 parameters are required, i.e. equilibrium dissociation constants (Ks, Ki, Ka, Kb, Kc, and Kd), a rate constant (k) and relative factors (e, f, and g).