RADIATION INACTIVATION SUGGESTS THAT HUMAN MULTIDRUG RESISTANCE-ASSOCIATED PROTEIN-1 OCCURS AS A DIMER IN THE HUMAN ERYTHROCYTE-MEMBRANE

Molecular masses of functional units of two components of 2,4-dinitrop henyl-S-glutathione (DNP-SG) transport across the erythrocyte membrane determined by radiation inactivation were 437 +/- 69 kDa for the high -affinity component and 466 +/- 67 kDa for the low-affinity component. These results confirm that the multidrug resistance-associated protei n (MRP) 1 is responsible for the high-affinity DNP-SG transport across the erythrocyte membrane and suggest that MRP1 exists in the membrane as a dimer, The molecular size of the low-affinity transporter is sim ilar if not identical to that of MRP1, Moreover, while the molecular m ass of the DNP-SG-ATPase activity of the erythrocyte membrane correspo nds also to that of MRP (375 +/- 36 kDa), the molecular mass of the fu nctional unit of dinitrophenol-stimulated ATPase is significantly lowe r (232 +/- 26 kDa), which suggests that this activity is linked to a d ifferent protein, perhaps aminophospholipid translocase. (C) 1998 Acad emic Press.