Activation energy of sulfate ion transport across methylated human erythrocyte membranes

Janas, Tadeusz; Kilian, Mieczysław; Przestalski, S.

doi:10.1016/0014-5793(88)80291-6

Cited by 3 publications

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“…A mitochondrial ADP/ATP carrier works at 0.05-0.1 sec −1 at 25°C (Schonfeld et al 1996), while the glucose transporter in human erythrocytes turns over at 600 sec −1 at 20°C (Stein 1990). The activation energy for protein transmembrane porters is usually in the range 40 to 130 kJ/mole, for example, sulfate ion transport by band 3 protein in human erythrocytes is at E A = 131 kJ/mole (Janas et al 1988) and, for the Glossina morsitans proline transporter, E A = 46 kJ/ mole (Njagi et al 1992). In this context, RNA (9:10 Trp ) at Ն0.25 sec −1 and 46 kJ/mole is both quantitatively and, by mechanism, comparable to slower protein transporters, and therefore appropriately called a tryptophan transporter made of RNA.…”

Section: Comparison To Proteinsmentioning

confidence: 99%

A membrane transporter for tryptophan composed of RNA

Janas¹,

Yarus²

2004

RNA

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We have incorporated an RNA binding site for the biological amino acid tryptophan within an RNA complex with affinity for phospholipid bilayer membranes. The resulting RNA (9:10 Trp ) creates a selective route through the bilayer for the amino acid. Binding and enhanced tryptophan permeability are nonlinear in RNA concentration, suggesting that RNA aggregation is required for both. Tryptophan permeability saturates with increased concentration, though at ∼ 1000-fold greater level than when binding a free aptamer. The RNA (9:10 Trp ) complex, bound at a mean of two per liposome, halves the activation energy for tryptophan transport (to 46 kJ/mole), specifically increasing tryptophan entry to a maximal velocity of 0.5 sec −1 per liposome with little or no accompanying increase in general permeability. Individual RNAs turn over tens of thousands of times at high tryptophan concentration. Thus, a specific passive membrane transporter whose properties overlap those of single-molecule transporter proteins, can be made of RNA alone. Permeability changes probably rely on disturbances in lipid conformation as well as on an advantageous low free energy position for tryptophan at the membrane. Other RNA activities may yield other RNA-membrane nanosystems via this route.

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Section: Comparison To Proteinsmentioning

confidence: 99%

A membrane transporter for tryptophan composed of RNA

Janas¹,

Yarus²

2004

RNA

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“…Functionally essential, positively charged arginyl residues with pK~12 were found in studies of the effects of extracellular pH on the exchange function [3] and by using chemical modification methods [4][5]. The results of Janas et al [6] indicate that the positively-charged lysine groups are not involved in the translocation step in anion exchange since the activation energy of sulfate transport is unchanged after reductive methylation of lysine residues of Band 3. The dependence of monovalent and divalent anion exchange on extracellular pH provided the first evidence for a functionally important carboxyl group(s).…”

Section: Introductionmentioning

confidence: 99%

Involvement of carboxyl groups in chloride transport and reversible DIDS binding to band 3 protein in human erythrocytes

Janas

2011

Cellular and Molecular Biology Letters

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Noncovalent DIDS binding to Band 3 (AE1) protein in human erythrocyte membranes, modified by non-penetrating, water soluble 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)-carbodiimide iodide (EAC), was studied at 0 o C in the presence of 165 mM KCl. Under experimental conditions applied up to (48 ± 5) % of irreversible chloride self-exchange inhibition was observed. The apparent dissociation constant, K D , for "DIDS-Band 3" complex, determined from the chloride transport experiments, was (34 ± 3) nM and (80 ± 12) nM for control and EAC-treated resealed ghosts, respectively. The inhibition constant, K i , for DIDS was (35 ± 6) nM and (60 ± 8) nM in control and EAC-treated ghosts, respectively. The reduced affinity for DIDS reversible binding was not a result of negative cooperativity of DIDS binding sites of Band 3 oligomer since Hill's coefficients were indistinguishable from 1 (within the limit error) both for control and EAC-treated ghosts. By using tritium-labeled DIDS, 4,4'-diisothiocyanato-2,2'-stilbenedisulfonate ( The results demonstrate that EAC modification of AE1 reduces about 2-fold the affinity of AE1 for DIDS. It is suggested that half of the subunits are modified near the transport site by EAC.

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Reversible DIDS binding to Band 3 protein in human erythrocyte membranes

Janas

2000

Molecular Membrane Biology

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Reversible binding of DIDS [4,4'-diisothiocyanato-2,2'-stilbenedisulphonate] to Band 3 protein, the anion exchanger located in erythrocyte plasma membrane, was studied in human erythrocytes. For this purpose, the tritiated form of DIDS ([3H]DIDS) has been synthesized and the filtering technique has been used to follow the kinetics of DIDS binding to the sites on Band 3 protein. The obtained results showed monophasic kinetics both for dissociation and association of the 'DIDS--Band 3' complex at 0 degree C in the presence of 165 mM KCl outside the cell (pH 7.3). A pseudo-first order association rate constant k+1 was determined to be (3.72 +/- 0.42) x 10(5) M-1 s-1, while the dissociation rate constant K-1 was determined to be (9.40 +/- 0.68) x 10(-3) s-1. The dissociation constant KD, calculated from the measured values of k-1 and k+1, was found to be 2.53 x 10(-8) M. The standard thermodynamics parameters characterizing reversible DIDS binding to Band 3 protein at 0 degree C were calculated. The mean values of the activation energies for the association and dissociation steps in the DIDS binding mechanism were determined to be (34 +/- 9) kJ mole-1 and (152 +/- 21) kJ mole-1, respectively. The results provide, for the first time, evidence for the reversibility of DIDS binding to Band 3 protein at 0 degree C. The existence of a stimulatory site is suggested, nearby the transport site on the Band 3 protein. The binding of an anion to this site can facilitate (through electrostatic repulsion interaction between two anions) the transmembrane movement of another anion from the transport site.

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Activation energy of sulfate ion transport across methylated human erythrocyte membranes

Cited by 3 publications

References 3 publications

A membrane transporter for tryptophan composed of RNA

A membrane transporter for tryptophan composed of RNA

Involvement of carboxyl groups in chloride transport and reversible DIDS binding to band 3 protein in human erythrocytes

Reversible DIDS binding to Band 3 protein in human erythrocyte membranes

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