Mn. Chernova et al., ELECTROGENIC SULFATE CHLORIDE EXCHANGE IN XENOPUS OOCYTES MEDIATED BYMURINE AE1 E699Q/, The Journal of general physiology, 109(3), 1997, pp. 345-360
Functional evaluation of chemically modified human erythrocytes has le
d to the proposal that amino acid residue E681 of the band 3 anion exc
hanger AE1 lies on the anion translocation pathway and is a proton car
rier required for H+/SO42- cotransport. We have tested in Xenopus oocy
tes the functional consequences of mutations in the corresponding resi
due E699 of mouse AE1. Most mutations tested abolished AE1-mediated Cl
- influx and efflux. Only the E699Q mutation increased stilbene disulf
onate-sensitive efflux and influx of SO42-. E699Q-mediated Cl- influx
was activated by elevation of intracellular SO42-, but E699Q-mediated
Cl- efflux was undetectable. The DNDS (4,4'-dinitrostilbene-2,2'-disul
fonic acid) sensitivity of E699Q-mediated SO42- efflux was indistingui
shable from that of wt AE1-mediated Cl- efflux. The extracellular anio
n selectivity of E699Q-mediated SO42- efflux was similar to that of wt
AE1-mediated Cl- efflux. The stoichiometry of E699Q-mediated exchange
of extracellular Cl- with intracellular SO42- was 1:1. Whereas SO42-
injection into oocytes expressing wt AE1 produced little change in mem
brane potential or resistance, injection of SO42-, but not of Cl- or g
luconate, into oocytes expressing E699Q depolarized the membrane by 17
mV and decreased membrane resistance by 66%. Replacement of bath Cl-
with isethionate caused a 28-mV hyperpolarization in SO42--loaded oocy
tes expressing E699Q but had no effect on oocytes expressing wt AE1. E
xtracellular Cl--dependent depolarization of SO42--preloaded oocytes w
as blocked by DNDS. AE1 E699Q-mediated inward current measured in the
presence of extracellular Cl- was of magnitude sufficient to account f
or measured (SO42-)-S-35 efflux. Thus, AE1 E699Q-mediated SO42-/Cl- ex
change operated largely, if not exclusively, as an electrogenic, asymm
etric, 1:1 anion exchange. The data confirm the proposal that E699 res
ides on or contributes to the integrity of the anion translocation pat
hway of AE1. A single amino acid change in the sequence of AE1 convert
ed electroneutral to electrogenic anion exchange without alteration of
SO42-/Cl- exchange stoichiometry.