A 24-state kinetic model of AdiC for transporting two types of ligand on opposite sides of the membrane. All states are denoted according to the sidedness configuration 1 described in Results. As an example, S₆ identified in the polarization study, which corresponds to the structural and functional state E_O, is denoted as ⁶E_O (bottom middle). The middle portion described the transition of apo AdiC among eight identified states differing in conformation or energy. The left and right portions describe the transport of the intracellular ligand L_I, e.g., Agm²⁺ or a nonradioactive ligand, and the extracellular ligand L_E, e.g., Arg⁺ or a radioactive ligand, respectively. As initial conditions, L_I is only present in the internal solution, whereas L_E is only present in the external solution. After being transported across the membrane, they are present on both sides. Transition rate constants k_i,j and k_j,i, associated with arrows, indicate the reversible transitions between corresponding states i and j (Tables S1, S2, S3, and S4). For distinction, the transitions involving the binding and unbinding of a ligand are labeled with $KD=koff/kon$⁠.