A membrane protein from human erythrocytes involved in anion exchange

Phosphate transport across the membrane of human erythrocytes, at pH 6.42, is a saturable process with an external Km of 80 mM and a Vmax of 2.8 mmol per liter of red cells per min. Transport is inhibited in a reversible manner by the sulfanilate anion and in an irreversible manner by the isothiocyanate derivative of the sulfanilate anion. This reagent reacts with only one membrane protein. When 300,000 molecules of reagent per cell are covalently attached to protein, transport is completely inhibited. This transport protein is a glycoprotein, it belongs to the general class designated as component a by Bretscher, and it therefore spans the bilayer. Transport does not involve movement of the protein around an axis parallel to the plane of the membrane.