Anion transport activity in the human erythrocyte membrane modulated by proteolytic digestion of the 38,000-dalton fragment in Band 3.

Extracellular treatment of human erythrocytes with papain completely converted the chymotryptic 38,000-dalton fragment of Band 3 to the 29,000-dalton fragment and inhibited the transport of inorganic phosphate in the cells. The inhibition, however, was not complete, indicating the presence of two components in the anion-transport system: the one resistant to papain digestion and the other sensitive to the digestion. The latter activity is well correlated with the degradation of the 38,000-dalton fragment. The activity remaining in the cells treated with papain was markedly different from that of the control cells. The remaining activity was not inhibited by pyridoxal phosphate and dinitrostilbene-2,2'-disulfonic acid, potent inhibitors to the anion transport, whereas phenyl phosphate inhibited the activities of both papain-treated and control cells. The results indicate that the anion-transport system consists of multiple anion-binding sites and a part of the system which is sensitive to pyridoxal phosphate and dinitrostilbene-2,2'-disulfonic acid was located in the papain-sensitive portion of 38,000-dalton fragment. A possible model of the anion-transport system was presented.