Substrate-induced conformational change of human erythrocyte glucose transporter: inactivation by alkylating reagents

The glucose transport carrier in human erythrocyte membranes, when transporting glucose, undergoes a conformation change. In an attempt to delineate the extent of this substrate-induced conformational change, transport inactivation by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, N-ethylmaleimide, iodoacetamide, and 2,4,6-trinitrobenzenesulfonic acid was examined in the presence and in the absence of D-glucose. All these alkylating agents inactivated the carrier. With each of these reagents, with the exception of trinitrobenzene-sulfonic acid, D-glucose modified the rate of inactivation as well as the activation enthalpy (delta H*) of the inactivation. The inactivation by trinitrobenzenesulfonic acid was not affected by the sugar. Based on these findings, it is suggested that the substrate-induced conformational change mostly occurs within the transmembrane hydrophobic domain while the hydrophilic extramembrane domains are largely outside of this change.