TRANSPORT AND MODIFIER SITES IN CAPNOPHORIN, THE ANION TRANSPORT PROTEIN OF THE ERYTHROCYTE MEMBRANE

Publisher Summary The transport and modifier sites are unified by the exchange zipper model, if it is assumed that the sites do not represent topographically separate entities, but reflect the cyclic variation of anion affinity at the external binding region. This chapter presents the model that shows the high and low affinity states of the external and internal anion binding sites that alternate with frequencies between 450 and 85,000 s -1 between 0 and 38 °C, that is, with the frequency of the anion exchange half-cycle. At low temperatures, there is a good chance that transport is ratelimited by the conformational change, which is responsible for the affinity shift. The inhibitory modifier effect is caused by anion-binding to the nontransporting, low affinity state, arresting the transport system in a trans-configuration.