EVIDENCE OF MULTIPLE OPERATIONAL AFFINITIES FOR D-GLUCOSE INSIDE THE HUMAN ERYTHROCYTE-MEMBRANE

1. 1. The Michaelis-Menten parameters of labelled d-glucose exit from human erythrocytes at 2°C into external solution containing 50 mM d-galactose were obtained. The Km is 3.4 ± 0.4 mM, V 17.3 ± 1.4 mmol · 1-1 cell water · min-1 for this infinite-trans exit procedure. 2. 2. The kinetic parameters of equilibrium exchange of d-glucose at 2°C are Km = 25 ± 3.4 mM, V 30 ± 4.1 mmol · 1-1 cell water · min-1. 3. 3. The Km for net exit of d-glucose into solutions containing zero sugar is 15.8 ± 1.7 mM, V 9.3 ± 3.3 mol 9.3 ± 3.3 mol · 1-1 cell water · min-1. 4. 4. This experimental evidence corroborates the previous finding of Hankin, B.L., Lieb, W.R. and Stein, W.D. [(1972) Biochim. Biophys. Acta 255, 126-132] that there are sites with both high and low operational affinities for d-glucose at the inner surface of the human erythrocyte membrane. This result is inconsistent with current asymmetric carrier models of sugar transport. © 1979.