Band 3 (AE1, SLC4A1)-mediated transport of stilbenedisulfonates. III: Role of solute and protein structure in proton-activated stilbenedisulfonate influx.

DBDS (4,4'-dibenzamido-2,2'-stilbenedisulfonate) influx into magnesium resealed ghosts (MRSG) occurs over the anion/proton co-transport pH range (pK approximately 5.0). Here, factors are studied which may influence the pH dependence of DBDS transport.

Band 3 (AE1, SLC4A1)-mediated transport of stilbenedisulfonates. I: Functional identification of the proton-activated stilbenedisulfonate influx site.

Stilbenedisulfonates (SD) bind to a "primary" SD (PSD) site on the outer membrane surface of band 3, and inhibit anion exchange (AE) allosterically. Yet, evidence [Membr. Biochem.

Band 3 (AE1, SLC4A1)-mediated transport of stilbenedisulfonates. II: Evidence for transmembrane allosteric interactions between the "primary" stilbenedisulfonate binding site and the stilbenedisulfonate efflux site.

Results from the first paper in this series indicated that the "primary" stilbenedisulfonate (PSD) site was not located on the DBDS (4, 4'-dibenzamido-2, 2'-stilbenedisulfonate) transport pathway into magnesium resealed ghosts (MRSG). Rather, transport correlated with DBDS binding to the "second" class of proton-activated binding sites located on the membrane domain of band 3 [Biochem. J.

Identification and characterization of a second 4,4'-dibenzamido-2,2'-stilbenedisulphonate (DBDS)-binding site on band 3 and its relationship with the anion/proton co-transport function.

Band 3 mediates both electroneutral AE (anion exchange) and APCT (anion/proton co-transport). Protons activate APCT and inhibit AE with the same pK (approximately 5.0).

The carboxyl side chain of glutamate 681 interacts with a chloride binding modifier site that allosterically modulates the dimeric conformational state of band 3 (AE1). Implications for the mechanism of anion/proton cotransport.

Glutamate 681 is thought to be located within the transport channel of band 3 (AE1, the chloride/bicarbonate exchanger), where it acts as a proton donor for the anion/proton cotransport function. Here we show that neutralization of the negative charge on glutamate 681 by chemically modifying band 3 with Woodward's reagent K plus sodium borohydride (i.e.