UNCOUPLERS OF MITOCHONDRIAL OXIDATIVE-PHOSPHORYLATION ARE NOT SUBSTRATES OF THE ERYTHROCYTE GLUTATHIONE-S-CONJUGATE PUMP

Uncouplers of mitochondrial oxidative phosphorylation, dinitrophenol ( DNP) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), we re found to stimulate Mg2+-ATPase activity of human erythrocyte membra nes in a manner competitive with respect to 2,4-dinitrophenyl-S-glutat hione (DNP-SG) which suggested that these compounds may also be substr ates of the glutathione-S-conjugate pump. We confirm that the stimulat ion of erythrocyte membrane ATPase activity by DNP and by another unco upler, carbonyl cyanide m-chlorophenylhydrazone (CCCP), is competitive with respect to DNP-SG, However, we found no evidence for active tran sport of DNP and CCCP out of erythrocytes and demonstrate that they in hibit the low-affinity component of DNP-SG transport noncompetitively while stimulating the high-affinity DNP-SG transport (mediated by mult idrug resistance-associated protein, MRP1), Implications of these find ings may indicate the electrogenic nature of MRP1-mediated transport o f glutathione-S conjugates and stimulation of aminophospholipid transl ocase (flippase) rather than the glutathione-S conjugate pump by the u ncouplers. (C) 1998 Academic Press.