AJP - Cell Physiology, Vol 260, Issue 3 C535-C544, Copyright © 1991 by American Physiological Society
Kinetics of DIDS inhibition of HL-60 cell anion exchange rules out ping-pong model with slippage
D. Restrepo, B. L. Cronise, R. B. Snyder, L. J. Spinelli and P. A. Knauf
Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104.
According to the ping-pong model of band 3-mediated anion exchange, the
transport protein has a single transport site, which can exist in either an
inward-facing or an outward-facing conformation. Anions bind to these
unloaded forms of the carrier, and translocation takes place only when a
suitable anion is bound to the transport site. In a previous paper [Am. J.
Physiol. 257 (Cell Physiol. 26): C520-C527, 1989], we had shown that the
substrate kinetics of Cl-Cl exchange in the promyelocytic HL-60 cell cannot
be explained by this simple ping-pong model of anion exchange but is
consistent with a simultaneous model according to which both extracellular
and intracellular anions must bind before simultaneous translocation can
take place. In the present paper we show that external
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibits anion
exchange in HL-60 cells by competing with Cl- for binding to the
outward-facing transport site. Furthermore, there is a linear dependence of
the slope of the Dixon plot for inhibition by DIDS on the reciprocal of the
intracellular Cl- concentration. This result clearly rules out a simple
ping-pong scheme. In addition, the data also rule out a ping-pong model in
which some translocation of the unloaded carrier is allowed (ping-pong
model with slippage). The observed inhibition kinetics can be modeled by a
simultaneous model of Cl-Cl exchange with competitive inhibition by DIDS.
