title: Co-operating ATP sites in the multiple drug resistance transporter Mdr1.
abstract: The ATPase activity of the multiple drug resistance transporter Mdr1 (P-glycoprotein, gp170) depended on the concentration of ATP with both positive and negative co-operativity both in the absence and in the presence of verapamil. Four co-operating binding sites for ATP were required to adequately model the experimental findings. The activation energy for the ATPase activity increased from approximately 385 kJ x mol-1 at 10 microM ATP to 512 kJ x mol-1 at 1600 microM, while changes in verapamil concentration had little effect. This indicates that the reaction mechanism of ATP hydrolysis depends on ATP concentration and is further evidence for co-operation of ATP binding sites. Free ATP in higher concentration was inhibitory; however, this inhibition could be reduced by complexing the ATP with Mg2+. Free Mg2+ had little effect on Mdr1 apart from complexing ATP.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, UK. engelbert@hsc.kuniv.edu.kw
authors.forename: E
authors.initials: E
authors.lastname: Buxbaum
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000494:Allosteric Regulation; D000818:Animals; D000911:Antibodies, Monoclonal; D001665:Binding Sites; D001692:Biological Transport; D016466:CHO Cells; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D006868:Hydrolysis; D008274:Magnesium / Q000378:metabolism; D008956:Models, Chemical; D013696:Temperature; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D000255:Adenosine Triphosphate; D014700:Verapamil; D000251:Adenosine Triphosphatases; D008274:Magnesium