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Abstract

The effects of a variety of chemically diverse, reversibly acting inhibitors have been measured on both Cl⁻ and SO₄²⁻ equilibrium exchange across the human red cell membrane. The measurements were carried out under the same conditions (pH 6.3, 8°C) and in the same medium for both the Cl⁻ and SO₂⁴ tracer fluxes. Under these conditions the rate constant for Cl⁻-Cl⁻ exchange is about 20 000 times larger than that for SO₄²⁻-SO₄²⁻ exchange. Despite this large difference in the rates of transport of the two anions, eight different reversibly acting inhibitors have virtually the same effect on the Cl⁻ and SO₄²⁻ transport. The proteolytic enzyme papain also has the same inhibitory effect on both the Cl⁻ and SO₄²⁻ self-exchange. In addition, the slowly penetrating disulfonate 2-(4′-aminophenyl)-6-methylbenzenethiazol-3′,7-disulfonic acid (APMB) is 5-fold more effective from the outer than from the inner membrane surface in inhibiting both Cl⁻ and SO₄²⁻ self-exchange. We interpret these results as evidence that the rapidly penetrating monovalent anion Cl⁻ and the slowly penetrating divalent anion SO₄²⁻ are transported by the same system.