Beschreibung:
<jats:p>The identification of the multidrug resistance protein (MRP) as a conjugate export pump in several cell types suggested its involvement in the long‐known glutathione‐<jats:italic>S</jats:italic>‐conjugate transport across erythrocyte membranes. We investigated the ATP‐dependent transport of glutathione <jats:italic>S</jats:italic>‐conjugates in human erythrocyte and erythroleukemia cell membrane vesicles using the endogenous conjugate leukotriene C<jats:sub>4</jats:sub> (LTC<jats:sub>4</jats:sub>), known to be a high‐affinity substrate for MRP, in addition to <jats:italic>S</jats:italic>‐(2,4‐dinitrophenyl)glutathione. The kinetic parameters, including the <jats:italic>K</jats:italic><jats:italic>m</jats:italic>, value for LTC<jats:sub>4</jats:sub> of 118 ± 5 nM and the inhibition constants for transport of both substrates for the quinoline‐based inhibitor MK 571, were similar to those obtained for transport mediated by recombinant MRP. Direct photoaffinity labeling of human erythrocyte membranes with [<jats:sup>3</jats:sup>H]LTC<jats:sub>4</jats:sub> revealed a major binding protein of about 190 kDa which was immunoprecipitated by an anti‐MRP serum. The radiolabeling of this protein was specifically suppressed by the transport inhibitor MK 571. Several additional anti‐MRP sera detected the protein of about 190 kDa in human erythrocyte and erythroleukemia cell membranes. These data identify for the first time the glutathione‐<jats:italic>S</jats:italic>‐conjugate transporting protein in erythrocyte membranes.</jats:p>