Interaction of phlorizin and sodium with the renal brush-border membrane D-glucose transporter: stoichiometry and order of binding.
The order and stoichiometry of the binding of phlorizin and sodium to the renal brush-border membrane D-glucose transporter are studied. The experimental results are consistent with a random-binding scheme in which the ratio of phlorizin- to sodium-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 microM at [Na] = 0 to 0.1 microM at [Na] = 100 mM and approaches 0.05 microM as [Na] leads to infinity. The experimental data are fit to a random carrier-type model of the coupled transport of sodium and D-glucose. A complete parameterization of the phlorizin binding properties of this model under sodium equilibrium conditions is given.
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004285:Dogs; D005947:Glucose / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D009005:Monosaccharides / Q000378:metabolism*; D010695:Phlorhizin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D002352:Carrier Proteins; D009004:Monosaccharide Transport Proteins; D009005:Monosaccharides; D012964:Sodium; D010695:Phlorhizin; D005947:Glucose