J. Biol. Chem., Vol. 263, Issue 1, 187-192, 01, 1988
High affinity phlorizin binding to the LLC-PK1 cells exhibits a sodium:phlorizin stoichiometry of 2:1
A Moran, LJ Davis and RJ Turner
Department of Physiology, Armed Forces Radiobiological Research Institute, Bethesda, Maryland 20892.
The phlorizin binding properties of luminal membrane vesicles isolated from
the LLC-PK1 cells, a continuous epithelial cell line derived from pig
kidney, are studied. Scatchard analysis of this binding indicates the
existence of a single high affinity sodium-dependent site with KD = 0.4
microM at 266 mM sodium. The specificity properties of this site indicate
that it represents the binding of phlorizin to the hexose binding site of
the sodium-dependent D-glucose transporter previously identified in this
cell line. Both phlorizin equilibrium binding and the rate of phlorizin
binding were found to be sigmoidal functions of sodium concentration. A
Hill analysis of these data was consistent with a sodium:phlorizin
stoichiometry of 2:1 in good agreement with the sodium:glucose
stoichiometry already established in these cells. Phlorizin dissociation
was also found to be sodium-dependent. On the basis of the phlorizin
binding data presented here, a number of models of the binding of phlorizin
and sodium to the transporter can be excluded. An analysis of a random
binding model consistent with the data is presented. The significance of
the LLC-PK1 sodium-dependent D- glucose transporter as a model system for
related renal and intestinal transporters is discussed.