Use of niflumic acid to determine the nature of the asymmetry of the human erythrocyte anion exchange system

Journal Article · Tue May 01 04:00:00 EDT 1984 · J. Gen. Physiol.; (United States)

DOI:https://doi.org/10.1085/jgp.83.5.703· OSTI ID:6194745

Knauf, P A; Mann, N A

Niflumic acid is a noncompetitive inhibitor of chloride exchange, which binds to a site different from the transport or modifier sites. When the internal Cl/sup -/ concentration is raised, at constant extracellular Cl/sup -/, the inhibitory potency of niflumic acid increases. This effect cannot be attributed to changes in membrane potential, but rather it suggests that niflumic acid binds to the anion exchange protein band 3 only when the transport site faces outward. When the chloride gradient is reversed, with Cl/sub o/ > Cl/sub i/, the inhibitory potency of niflumic acid decreases greatly, which indicates that the affinity of niflumic acid for band 3 with the transport site facing inward is almost 50 times less than when the transport site faces outward. Experiments in which Cl/sub i/ = Cl/sub o/ show no significant change in the inhibition by niflumic acid when Cl/sup -/ is lowered from 150 to 10 mM. These data suggest that the intrinsic dissociation constants for Cl/sup -/ at the two sides of the membrane are nearly equal. Thus, the chloride-loaded transport sites have an asymmetric orientation like that of the unloaded transport sites, with approx.15 times more sites facing the inside than the outside. The asymmetry reflects an approx.1.5 kcal/mol free energy difference between the inward-facing and outward-facing chloride-loaded forms of band 3. High concentrations of chloride (with Cl/sub i/ = Cl/sub o/), which partially saturate the modifier site, have no effect on niflumic acid inhibition, which indicates that chloride binds equally well to the modifier site regardless of the orientation of the transport site. 25 references, 6 figures, 3 tables.

• Research Organization: Univ. of Rochester School of Medicine, NY
• OSTI ID: 6194745
• Journal Information: J. Gen. Physiol.; (United States), Journal Name: J. Gen. Physiol.; (United States) Vol. 83; ISSN JGPLA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
ANIONS
AZINES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
CHLORIDES
CHLORINE COMPOUNDS
DATA
ERYTHROCYTES
EXPERIMENTAL DATA
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
ION EXCHANGE
IONS
KINETICS
MAMMALS
MAN
MATERIALS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
MEMBRANES
NICOTINIC ACID
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PRIMATES
PROTEINS
PYRIDINES
REACTION KINETICS
RECEPTORS
USES
VERTEBRATES
VITAMIN B GROUP
VITAMINS