Failure of equilibrium dialysis to show selective monosaccharide binding by erythrocyte membranes.

Equilibrium dialysis has been reported to show stereoselective binding of the preferred sugar transport substrate,D-glucose, by NaI protein extracts of human erythrocyte membranes. However, we were unable to show any detectable differential binding ofD-glucose (as compared with the poorly transported analogue,L-sorbose) with NaI protein extracts. The basis for this decided dissonance is not clear. Extracts with nonionic detergents, various alcohols, and pyridine were also used, but the results with these were also negative. Our data indicate either that the transport sites are not thus extractable in a functional condition, or that only a very small number of binding sites (less than 100,000) are involved with the sugar translocation; and that this method cannot serve to measure the site population unless a far greater concentration of the binding material can be achieved than has so far been possible.