IDENTIFICATION OF THE MULTIDRUG-RESISTANCE PROTEIN (MRP) AS THE GLUTATHIONE-S-CONJUGATE EXPORT PUMP OF ERYTHROCYTES

The identification of the multidrug resistance protein (MRP) as a conj ugate export pump in several cell types suggested its involvement in t he long-known glutathione-S-conjugate transport across erythrocyte mem branes. We investigated the ATP-dependent transport of glutathione S-c onjugates in human erythrocyte and erythroleukemia cell membrane vesic les using the endogenous conjugate leukotriene C-4 (LTC(4)), known to be a high-affinity substrate for MRP, in addition to S-(2,4-dinitrophe nyl)glutathione. The kinetic parameters, including the K-m value for L TC(4) of 118 +/- 5 nM and the inhibition constants for transport of bo th substrates for the quinoline-based inhibitor MK 571, were similar t o those obtained for transport mediated by recombinant MRP. Direct pho toaffinity labeling of human erythrocyte membranes with [H-3]LTC(4) re vealed a major binding protein of about 190 kDa which was immunoprecip itated by an anti-MRP serum. The radiolabelling of this protein was sp ecifically suppressed by the transport inhibitor MK 571. Several addit ional anti-MRP sera detected the protein of about 190 kDa in human ery throcyte and erythroleukemia cell membranes. These data identify for t he first time the glutathione-S-conjugate transporting protein in eryt hrocyte membranes.