Effect of ADP on Na+-Na+ Exchange Reaction Kinetics of Na,K-ATPase

Peluffo, R. Daniel

doi:10.1529/biophysj.103.030643

Cited by 17 publications

(20 citation statements)

References 51 publications

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“…In the outward-facing conformation, Na + release is followed by binding of K + in the normal forward operation of the Na/K pump, inducing an outwardly directed pump current that can be studied under voltage clamp. Rebinding of Na Most of the cycle's voltage dependence is believed to arise from the release (rebinding in the backward reaction) of the first Na + ion through a high-field access channel when leaving its binding site (3,4,7). There are indications that the Na + -exclusive site III releases Na + before the shared sites (6,8,9) and that the voltagedependent rebinding of this first externally released Na + blocks release of the other two Na + ions from the shared sites.…”

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confidence: 99%

Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations

Ratheal

Virgin

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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The Na/K pump is a P-type ATPase that exchanges three intracellular Na + ions for two extracellular K + ions through the plasmalemma of nearly all animal cells. The mechanisms involved in cation selection by the pump's ion-binding sites (site I and site II bind either Na + or K + ; site III binds only Na + ) are poorly understood. We studied cation selectivity by outward-facing sites (high K + affinity) of Na/K pumps expressed in like organic cation transport challenges the concept of rigid structural models in which ion specificity at site I and site II arises from a precise and unique arrangement of coordinating ligands. Furthermore, actions by guanidinium + derivatives suggest that Na + binds to site III in a hydrated form and that the inward current observed without external Na + and K + represents cation transport when normal occlusion at sites I and II is impaired. These results provide insights on external ion selectivity at the three binding sites.he Na/K pump uses the free energy from ATP hydrolysis to export three Na + ions against a steep electrochemical gradient in exchange for the import of two K + ions. The pump alternates between two major conformational states, E1 and E2 (1), and its function is explained via a ping-pong (2) alternate-access mechanism (Fig. S1). Under physiological conditions, the E2P (phosphorylated) state, with extracellular-facing ion-binding sites, must select K + in the presence of more than 10-fold greater external Na + concentration. On the other hand, the E1 state, with cytoplasmic-facing ion-binding sites, selects Na + over K + , which is present at a 10-fold higher concentration.Of the three ion-binding sites, sites I and II, or shared sites, can bind either Na + or K + , but site III exclusively binds Na + . External release of Na + ions from these three sites occurs sequentially (3, 4). In the outward-facing conformation, Na + release is followed by binding of K + in the normal forward operation of the Na/K pump, inducing an outwardly directed pump current that can be studied under voltage clamp. Rebinding of Na Most of the cycle's voltage dependence is believed to arise from the release (rebinding in the backward reaction) of the first Na + ion through a high-field access channel when leaving its binding site (3, 4, 7). There are indications that the Na + -exclusive site III releases Na + before the shared sites (6,8,9) and that the voltagedependent rebinding of this first externally released Na + blocks release of the other two Na + ions from the shared sites. Concordantly, at saturating [K + o ], where Na + competition for the shared sites should be negligible, the Na/K pump current still presents significant VDI in the presence of external Na + (10) (Fig. S2). In addition, several studies have proposed a noncanonical mode of transport in which protons move in the inward direction down their electrochemical gradient at very negative voltages (11) through a pathway that passes through site III (9, 10, 12, 13).These observations raise a number of critical questions ...

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mentioning

confidence: 99%

Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations

Ratheal

Virgin

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…An example is the 9-state model of the Na,K-ATPase. 16 Thus Fig. 2 Step 2: The gross rate constants s i,j of the individual branches between S a and S b have to be added (compare Eq.…”

Section: Calculation Of the Occupation Probabilities And Of The Currentmentioning

confidence: 99%

“…Using gross rate constants also for the second branch (and additional ones) may become necessary, for instance, for a 9-state scheme of the Na C /K C pump. 16 Step 3: Knowing the gross rate constants g a,b and g b,a the matrices Dg CnÃ j can be generated, as shown for (50) The long arrows between S a and S b are the gross rate constants g a,b and g b,a without reserve factors.…”

Section: Calculation Of the Occupation Probabilities And Of The Currentmentioning

confidence: 99%

“…Reaction kinetic analysis of ion transport on the basis of such a model yields the rate constants of loading of the transport site, the velocity of the electro-sensitive translocation step, the influence of substrate concentrations or of ATP on these parameters, 7-13 the occupation probability of intermediate (structural) states of the protein, 11 charge of the translocated complex, 14 binding order in the case of cotransporters and pumps. 6,15,16 Hills et al 5 even developed a computer program to model an ensemble of transport molecules in order to describe the transport physiology of an entire guard cell.…”

Section: Introductionmentioning

confidence: 99%

“…11 Of special interest are cyclic reaction schemes. It is immediately obvious that they apply to electrogenic pumps 3,8,12,13,16,19,22 and cotransporters. 6,14,15,23,24 However, it turned out that cyclic reaction schemes also provided the best fits of IV curves from ion channels, 7,[25][26][27] from bacteriorhodopsin, 9,17 the viral M2 channel 11 or from Polytheonamide B, a marine cytotoxic b-helical peptide.…”

Section: Introductionmentioning

confidence: 99%

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A simple recipe for setting up the flux equations of cyclic and linear reaction schemes of ion transport with a high number of states: The arrow scheme

2016

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The calculation of flux equations or current-voltage relationships in reaction kinetic models with a high number of states can be very cumbersome. Here, a recipe based on an arrow scheme is presented, which yields a straightforward access to the minimum form of the flux equations and the occupation probability of the involved states in cyclic and linear reaction schemes. This is extremely simple for cyclic schemes without branches. If branches are involved, the effort of setting up the equations is a little bit higher. However, also here a straightforward recipe making use of so-called reserve factors is provided for implementing the branches into the cyclic scheme, thus enabling also a simple treatment of such cases.

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The Effect of Holding Potential on Charge Translocation by the Na+/K+-ATPase in the Absence of Potassium

Ding

Rakowski

2010

J Membrane Biol

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The Na(+)/K(+)-ATPase exports 3Na(+) and imports 2K(+) at the expense of the hydrolysis of 1 ATP. In the absence of K(+), it carries on electroneutral, Na(+)-dependent transient charge movement (also known as "electroneutral Na(+)/Na(+) exchange mode") and produces a transient current containing faster and slower components in response to a sudden voltage step. Components with different speeds represent sequential release of Na(+) ions from three binding sites. The effect of holding potential on slow charge movement was studied in the presence of different concentrations of ADP(i), Na (i) (+) and Na (o) (+) with the intention of improving our understanding of Na (i) (+) binding. However, the manipulation of [ADP](i) and [Na(+)](i) did not cause as pronounced changes as predicted in the magnitude of charge movement (Q (tot)), which indicated that our experimental conditions were not able to backwardly drive reaction across the energy barrier to Na (i) (+) release/rebinding steps. On the contrary, lowering [Na(+)](o) caused evident dependence of Q (tot) on holding potential, with characteristics suggesting that pumps were escaping from E2P through the uncoupled Na(+) efflux activity.

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Effect of ADP on Na+-Na+ Exchange Reaction Kinetics of Na,K-ATPase

Cited by 17 publications

References 51 publications

Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations

Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations

A simple recipe for setting up the flux equations of cyclic and linear reaction schemes of ion transport with a high number of states: The arrow scheme

The Effect of Holding Potential on Charge Translocation by the Na+/K+-ATPase in the Absence of Potassium

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