Interaction of alcohols with the transport system of glucose in human erythrocytes

Alcohols inhibit the exchange transport of glucose in human erythrocytes. Comparing the inhibition by monohydroxy-alcohols, which have different distribution coefficients between medium and membrane, shows that the degree of inhibition depends mainly upon the concentration of the alcohol in the membrane. 1-butanol exerts a mixed-type inhibition; V_max decreases and K_m increases. Since also the K_m of the equilibrium transport increases upon the addition of the alcohol, the changes in the K_m of exchange transport cannot be attributed solely to the differently affected mobilities of the loaded and free carrier, but the affinity of glucose to the transport system is reduced. The transport system can bind two alcohol molecules. With one alcohol molecule bound the affinity of the transport system for the second alcohol molecule already increases. The nature of the bond of the alcohols to the transport system is discussed and possible explanations for the cooperative effect upon the binding of the second alcohol molecule are offered.