The Journal of General Physiology, Vol 79, 169-185, Copyright © 1982 by The Rockefeller University Press
Stoichiometry of a half-turnover of band 3, the chloride transport protein of human erythrocytes
ML Jennings
The kinetics of human red blood cell Cl transport have been studied under
nonequilibrium conditions to determine whether or not an outward Cl
gradient can recruit the transport protein from an inward-facing to an
outward-facing configuration. Three kinds of evidence are consistent with
this outward recruitment. First, the initial net Cl efflux into a Cl-free
phosphate medium is independent of the intracellular Cl concentration in
the range 20-170 mM. Second, an outward Cl gradient strongly enhances the
inhibitory potency of DNDS (4,4'-dinitro-2,2'- stilbene disulfonate), which
suggests that DNDS binds primarily to outward-facing states. Finally, we
have estimated the number of Cl ions transported during the putative
outward recruitment. Resealed red cell ghosts containing only 70 muM 36Cl
were resuspended at 0 degrees C in a Cl-free, HCO3-free Na2SO4 medium. In
the first 10 s, or approximately 10(6) Cl ions per ghost, followed by a
much slower further loss of Cl. The rapid loss of 10(6) Cl ions per ghost,
which is abolished by pretreatment with DIDS
(4,4'-diisothiocyano-2,2'-stilbene disulfonate), appears to represent the
Cl that is transported during the first half- turnover of the transport
cycle. These data are strong evidence that the influx and efflux events in
the catalytic cycle for anion transport do not take place simultaneously,
and that the stoichiometry of the transport cycle is close to one pair of
anions exchanged per band 3 monomer.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
