The role of the surface energy of water in the conformational changes of the human erythrocyte glucose transporter.

There is now strong experimental evidence that the red cell glucose transporter protein operates by a conformational change which has the effect of presenting a sugar binding site to the outside and inside medium of the cells in an alternating manner, but the way in which this is brought about is still unknown. Kinetic evidence that the conformational changes which create the inward and outward facing modes can occur in the absence of a sugar substrate has been put on a firmer experimental basis by Appleman and Lienhard (1989). Conformational changes of the magnitude envisaged are too large to be attributed only to spontaneous thermal agitation in the protein. Theoretical considerations show that the surface energy of water could be an alternative source of energy which, in a suitable reciprocating cycle of activity, could sustain the conformational changes throughout the existence of the transporter.