Effects of the transport site conformation on the binding of external NAP-taurine to the human erythrocyte anion exchange system: evidence for intrinsic asymmetry
External N-(4-azido (NAP-taurine) inhibits human red cell chloride exchange by binding to a site that is distinct from the chloride transport site. Increases in the intracellular chloride concentration (at constant external chloride) cause an increase in the inhibitory potency of external NAP-taurine. This effect is not due to the changes in pH or membrane potential that usually accompany a chloride gradient, since even when these changes are reversed or eliminated the inhibitory potency remains high. According to the ping-pong model for anion exchange, such transmembrane effects of intracellular chloride on external NAP-taurine can be explained if NAP-taurine only binds to its site when the transport site is in the outward-facing (E/sub o/ or ECl/sub o/) form. Since NAP-taurine prevents the conformational change from ECl/sub o/ to ECl/sub i/, it must lock the system in the outward-facing form. NAP-taurine can therefore be used just like the competitive inhibitor H/sub 2/DIDS (4,4'-diisothiocyano-1,2-diphenylethane-2,2'-disulfonic acid) to monitor the fraction of transport sites that face outward. A quantitative analysis of the effects of chloride gradients on the inhibitory potency of NAP-taurine and H/sub 2/DIDS reveals that the transport system is intrinsically asymmetric, such that when Cl/sub i/ = Cl/sub o/, most of the unloaded transport sites face the cytoplasmic side of the membrane. 30 references, 7 figures, 3 tables.
- Research Organization:
- Research Institute, Toronto, Ontario
- OSTI ID:
- 6188883
- Journal Information:
- J. Gen. Physiol.; (United States), Vol. 83
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
CHLORIDES
MEMBRANE TRANSPORT
ION EXCHANGE
MATHEMATICAL MODELS
TAURINE
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
ANIONS
CELL MEMBRANES
ERYTHROCYTES
EXPERIMENTAL DATA
INHIBITION
PH VALUE
AMINES
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CELL CONSTITUENTS
CHARGED PARTICLES
CHLORINE COMPOUNDS
DATA
HALIDES
HALOGEN COMPOUNDS
INFORMATION
IONS
KINETICS
MATERIALS
MEMBRANES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
REACTION KINETICS
SULFONIC ACIDS
560301* - Chemicals Metabolism & Toxicology- Cells- (-1987)
550200 - Biochemistry