Anion exchange in human erythrocytes has a large activation volume

Sulfate equilibrium exchange in human red cells has an activation volume of +150 +/- 20 cm3/mol over the pressure range 0.1 to 83 MPa (15 to 12000 lb/in2) at 30 degrees C. This value greatly exceeds the expected contribution from sulfate binding to the anion exchanger. We suggest that the activation volume reflects conformational changes during the transport cycle.