A general kinetic analysis of transport Tests of the carrier model based on predicted relations among experimental parameters

Devés, R.; Krupka, Richard M.

doi:10.1016/0005-2736(79)90139-1

Cited by 58 publications

(42 citation statements)

References 15 publications

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“…I, and C, is the total carrier concentration, [C,,] + [Ci]. The required correction factor, I + f_J f~, can be determined by experiment, for the flux ratio may be shown to have exactly the same dependence on the equilibrium carrier partition, f_ I/ft [2]:…”

Section: Discussionmentioning

confidence: 99%

The choline carrier of erythrocytes: Location of the NEM-reactive thiol group in the inner gated channel

Krupka

Devés

1988

J. Membrain Biol.

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Choline transport across the human erythrocyte membrane is irreversibly inhibited when N-ethylmaleimide (NEM) reacts with a carrier SH group which is located outside the substrate site, and which is exposed in the inward-facing form of the carrier but prevented from reacting in the outward-facing form. The location of the SH group with respect to the membrane has now been determined by studying the dependence of the NEM-alkylation rate on the intracellular and extracellular pH. The results show that the reactive SH group equilibrates with hydrogen ions in the cytoplasm, but is completely isolated from hydrogen ions in the external medium. With this added evidence it becomes possible to conclude that the SH group is located in the inner gated channel of the choline carrier.

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Section: Discussionmentioning

confidence: 99%

The choline carrier of erythrocytes: Location of the NEM-reactive thiol group in the inner gated channel

Krupka

Devés

1988

J. Membrain Biol.

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“…In the Iatter case, the equation is easily verified by substituting f3 = f-3 = 0 into Eqs. (1) (6) and (7), the inactivation rate is found to be…”

Section: The Carrier Distribution Is Directly Related To the Substratmentioning

confidence: 96%

The comparative specificity of the inner and outer substrate transfer sites in the choline carrier of human erythrocytes

Devés

Krupka

1984

J. Membrain Biol.

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The substrate specificities on the inner and outer surfaces of the cell membrane have been compared by determining the relative affinities, inside and outside, of a series of choline analogs. The results of two different methods were in agreement: (1) the carrier distribution was determined in the presence of a saturating concentration of an equilibrated analog, using N-ethylmaleimide as a probe for the inward-facing carrier; (2) the degree of competition was measured between an equilibrated analog and choline in the external solution. The carrier sites are found to have markedly different specificities: the outer site is more closely complementary to the structure of choline than is the inner, and even a slight enlargement of either the trimethylammonium or hydroxyethyl group gives rise to preferential binding inside. It is also found that a nonpolar binding region, which is adjacent to the outer site, is absent from the inner site. As the transport mechanism involves the exposure of only one site at a time, first on one surface and then the other, it follows that an extensive reorganization of the structure of the substrate site may occur during the carrier-reorientation step, or alternatively that two distinct sites may be present, only one of which is exposed at a time.

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“…A general derivation of this equation was presented earlier [2]. Equation (8) indicates that the rate increase on addition of external substrate depends on the partition of the free carrier in the undisturbed system: if the carrier is predominantly inward-facing ([C/] -~ [Ct]), external substrate should have little or no effect, but if it is predominantly outward-…”

Section: ) _ [G] + [Co] _ 1 + [Comentioning

confidence: 99%

“…Substitution of these inequalities into general expressions for the maximum rates of zero-trans entry (Vso) and zero-trans exit Vsi) yields the following simple equations [2,11]:…”

Section: Effect Of Ph On the Mobility Of The Free Carriermentioning

confidence: 99%

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The carrier reorientation step in erythrocyte choline transport: pH effects and the involvement of a carrier ionizing group

1986

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Under zero-trans conditions, the facilitated transport of choline across the erythrocyte membrane is limited by the rate of reorientation of the free carrier; as a result the pH dependence of this step can be investigated, independent of other steps in transport. It is found that as the pH declines (between 8.0 and 6.0) the rate of inward movement of the free carrier rises and the rate of outward movements falls, so that the partition of the free carrier increasingly favors the inward-facing form. When the pH of the cell interior and of the medium are varied independently, the partition responds to the internal but not the external pH. The membrane potential, which varies somewhat as the pH is altered, has no effect on the carrier partition. The analysis of the results indicates that the carrier mobility is dependent on an ionizing group of pKa 6.8, which is exposed on the cytoplasmic surface of the membrane in the inward-facing carrier; in the outward-facing carrier the ionizing group appears to be masked, in that its pKa is shifted downward by more than one unit. The observations can be explained by assuming that an ionizing group is located in the wall of a gated channel connecting the substrate site with the cytoplasmic face of the cell membrane.

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A general kinetic analysis of transport Tests of the carrier model based on predicted relations among experimental parameters

Cited by 58 publications

References 15 publications

The choline carrier of erythrocytes: Location of the NEM-reactive thiol group in the inner gated channel

The choline carrier of erythrocytes: Location of the NEM-reactive thiol group in the inner gated channel

The comparative specificity of the inner and outer substrate transfer sites in the choline carrier of human erythrocytes

The carrier reorientation step in erythrocyte choline transport: pH effects and the involvement of a carrier ionizing group

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