Interaction of phlorizin and sodium with the renal brush-border membraned-glucose transporter: Stoichiometry and order of binding

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Abstract
The order and stoichiometry of the binding of phlorizin and sodium to the renal brush-border membraned-glucose transporter are studied. The experimental results are consistent with a random-binding sites is one-to-one. When the kinetics of phlorizin binding are measured as a function of increasing sodium concentration no significant variation is found in the apparent number of binding sites; however, the apparent binding constant for phlorizin decreases rapidly from approximately 16 μm at [Na]=0 to 0.1 μm at [Na]=100mm and approaches 0.05 μm as [Na]→∞. The experimental data are fit to a random carrier-type model of the coupled transport of sodium andd-glucose. A complete parameterization of the phlorizin binding properties of this model under sodium equilibrium conditions is given.