RECONSTITUTION OF PURIFIED P-GLYCOPROTEIN INTO LIPOSOMES

To study the molecular function of the multidrug-resistance gene product P-glycoprotein, we purified and reconstituted it into liposomes. Twelve detergents were examined in an attempt to solubilize and reconstitute the transport activity of K562/ADM membrane proteins containing P-glycoprotein. We found that transport activity was effectively reconstituted after solubilization with cholate, glycocholate and taurocholate. Other detergents, such as CHAPS, Triton X-100 and deoxycholate, diminished the transport activity. The K562/ADM membrane was solubilized by 1% glycocholate, and P-glycoprotein was purified by MRK-16 immunoaffinity column chromatography to a homogeneous single band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The purified P-glycoprotein was reconstituted by detergent dialysis into liposomes composed of phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine. The reconstituted P-glycoprotein specifically bound [H-3]azidopine and had an ATPase activity that was slightly stimulated when vincristine was added. Furthermore, though its activity was reduced, the reconstituted P-glycoprotein was shown to be an ATP-dependent transporter of vincristine.