Fig. 2.

Rapid equilibrium model of Na-K-2Cl cotransport with one of the Cl⁻ ions binding first. A: order of ion binding is different from the order of ion binding in Fig. 1, and the dissociation constants have been reassigned accordingly. B: simulation of Lineweaver-Burke plot of K⁺ influx⁻¹ vs. [Na⁺]_o⁻ based on Eq. 9 demonstrates that with this order of ion binding, the flux is dependent upon external Na⁺. The intercept of the lines in the left quadrant, which represents the reciprocal of the apparent affinity for Na⁺, is located within the range of the plot. Simulation was done with K1 set at 1 mM, K2 set at 25 mM, K3 set at 200 mM, and K4 set at 2 mM.