Fig. 1.

A Conventional representation of the symmetrical carrier model with the Kⁱⁿ_D = K^out_D = 3 mmol/L and kC_out–in = kC_in–out. The thicker arrows represent higher flow rates of liganded carrier than those of the empty carrier. The blue arrows represent the influx pathway and the red arrows the efflux pathway. The symmetrical rates of ligand carrier transit kGC_out–in, kGC_out–in are 10× faster than the fast rate of empty carrier movement kC_out–in, the second-order rates of ligand association with the external and internal carrier forms, G_outk_out and G_ink_in are assigned to be 1000× faster than kC_out–in. B Conventional representation of the asymmetric alternating transporter model with parameters as illustrated in D. The simulation shows that V_m = 1.6 nmol/(L·s) for zero-trans- net influx with the parameters as in D is approximately 33% of the V_m for exchange uptake = 4.8 nmol/(L·s) and the K_m for net influx = 1.0 mmol/(L·s) is approximately 20% of the K_m for exchange influx = 5.0 mmol/L. The V_m for net efflux = 6.3 nmol/(L·s), i.e. 3.9× faster than net influx. C Jardetzky adaptation of gated asymmetric transporter. D Asymmetric single-cycle alternating carrier model. The lengths of the vertical lines represent the relative rates of association and dissociation. The relative lengths and widths of the horizontal lines represent the relative transit rates of loaded and unloaded carrier forms. The angular displacements of the horizontal rates represent the Gibbs free energy differences between the states. The free energy differences between liganded and unliganded states are not displayed. E Equations showing how asymmetric affinities of a single-cycle carrier enforce asymmetric rates of empty carrier distribution