Characterization of oxalate transport by the human erythrocyte band 3 protein

Abstract

This paper describes characteristics of the transport of oxalate across the human erythrocyte membrane. Treatment of cells with low concentrations of H2DIDS (4,4'-diisothio-cyanatostilbene-2,2'- disulfonate) inhibits (3-Cl and oxalate-oxalate exchange to the same extent, suggesting that band 3 is the major transport pathway for oxalate. The kinetics of oxalate and Cl self-exchange fluxes indicate that the two ions compete for a common transport site; the apparent Cl affinity is two to three times higher than that of oxalate. The net exchange of oxalate for Cl, in either direction, is accompanied by a flux of H+ with oxalate, as is also true of net Cl - SO4/2 exchange. The transport of oxalate, however, is much faster than that of SO4/2 or other divalent anions. Oxalate influx into Cl -containing cells has an extracellular pH optimum of ~5.5 at 0°C. At extracellular pH below 5.5 (neutral intracellular pH), net Cl -oxalate exchange is nearly as fast as Cl -Cl exchange. The rapid Cl -oxalate exchange at acid extracellular pH is not likely to be a consequence and Cl exchange for monovalent oxalate (HOOC-COO ; pK(a) = 4.2) because monocarboxylates of similar structure exchange for Cl much more slowly than does oxalate. The activation energy of Cl -oxalate exchange is about 35 kCal/mol at temperatures between 0 and 15°C; the rapid oxalate influx is therefore not a consequence of a low activation energy. The protein phosphatase inhibitor okadaic acid has no detectable effect on oxalate self-exchange, in contrast to a recent finding in another laboratory (Baggio, B., L. Bordin, G. Clari, G. Gambaro, and V. Moret, 1993. Biochim. Biophys. Acta. 1148:157-160); our data provide no evidence for physiological regulation of anion exchange in red cells.