WW-781, a potent reversible inhibitor of red cell Cl- flux, binds to band 3 by a two-step mechanism.
WW-781 ([3-methyl-1-p-sulfophenyl-5-pyrazolone-(4)]-[1,3-dibutylbarbit uric acid]-pentamethine oxonol), a fluorescent dye that has been used for measuring membrane potentials by optical methods, inhibits human red blood cell Cl- exchange, which is mediated by the membrane protein known as band 3 or capnophorin. The inhibition is slowly reversible upon removal of WW-781 from the medium, with a half time of approximately 4.7 min in 150 mM Cl- medium at 0 degrees C. The mechanism of inhibition by WW-781 involves a two-step binding reaction. WW-781 binds rapidly to band 3 to form an initial complex, which can also rapidly dissociate. Formation of this initial complex is followed by the much slower formation of a second complex (with a rate constant of approximately 1.1 min-1), probably involving a protein conformational change, through which WW-781 is more tightly bound to band 3. At low concentrations, WW-781 inhibits Cl- exchange with a stoichiometry of 1 WW-781 molecule per band 3 monomer, suggesting that under these conditions the binding of WW-781 is highly selective for the band 3 protein.
Raha
N M
NM
Department of Biophysics, University of Rochester Medical Center, New York 14642.
Spinelli
L J
LJ
Knauf
P A
PA
D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D001557:Benzenesulfonates / Q000378:metabolism* / Q000494:pharmacology; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D007474:Ion Exchange; D008954:Models, Biological
D001457:Anion Exchange Protein 1, Erythrocyte; D001557:Benzenesulfonates; D002712:Chlorides; C031916:WW-781