Osmotic Stress and Viscous Retardation of the Na,K-ATPase Ion Pump

Esmann, Mikael; Fedosova, Natalya U.; Marsh, Derek

doi:10.1529/biophysj.106.101774

Cited by 25 publications

(24 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This value is consistent with previous studies using other methods (23)(24)(25)27). Under the same pH and ionic strength conditions, Mg 2+ was found to bind to ATP in free solution with a dissociation constant of 71 ( (3) µM.…”

Section: Discussionsupporting

confidence: 91%

“…The results of a titration of shark Na The results of these simulations (see Figure 3) show that a monomeric model in the absence of Mg 2+ ions predicts a hyperbolic saturation curve of the ATP sites, with halfsaturation occurring in the submicromolar range, in agreement with experimental observations (23)(24)(25)27). One needs to be aware here that the actual half-saturating concentration depends on how the theoretical or experimental data are plotted.…”

Section: Binding Of Mgsupporting

confidence: 72%

See 1 more Smart Citation

ATP Binding Equilibria of the Na⁺,K⁺-ATPase

et al. 2008

View full text Add to dashboard Cite

Reported values of the dissociation constant, K d , of ATP with the E1 conformation of the Na + ,K + -ATPase fall in two distinct ranges depending on how it is measured. Equilibrium binding studies yield values of 0.1-0.6 µM, whereas presteady-state kinetic studies yield values of 3-14 µM. It is unacceptable that K d varies with the experimental method of its determination. Using simulations of the expected equilibrium behavior for different binding models based on thermodynamic data obtained from isothermal titration calorimetry we show that this apparent discrepancy can be explained in part by the presence in presteady-state kinetic studies of excess Mg 2+ ions, which compete with the enzyme for the available ATP. Another important contributing factor is an inaccurate assumption in the majority of presteady-state kinetic studies of a rapid relaxation of the ATP binding reaction on the time scale of the subsequent phosphorylation. However, these two factors alone are insufficient to explain the previously observed presteady-state kinetic behavior. In addition one must assume that there are two E1-ATP binding equilibria. Because crystal structures of P-type ATPases indicate only a single bound ATP per R-subunit, the only explanation consistent with both crystal structural and kinetic data is that the enzyme exists as an (R ) 2 diprotomer, with protein-protein interactions between adjacent R-subunits producing two ATP affinities. We propose that in equilibrium measurements the measured K d is due to binding of ATP to one R-subunit, whereas in presteadystate kinetic studies, the measured apparent K d is due to the binding of ATP to both R-subunits within the diprotomer.Throughout the animal kingdom, the Na + ,K + -ATPase is responsible for pumping Na + and K + ions across the plasma membrane and thus maintaining electrochemical potential gradients for both ions across the membrane. A major function of the Na + electrochemical potential gradient is to act as a driving force for the uptake of essential metabolites such as glucose and amino acids. Probably the most enduring controversy in the Na + ,K + -ATPase 1 field is whether the enzyme functions as a monomer, dimer, or higher oligomer (1, 2). The idea that the functional unit of the Na + ,K + -ATPase might consist of an association of two protein monomers was first proposed in the 1970s (3,4). Since then, the idea has had many supporters (5-16) but also some vocal critics (17)(18)(19)(20)(21)(22) so that the hypothesis of a functional Na + ,K + -ATPase dimer or higher oligomer has never been universally accepted.One of the puzzling observations in the Na + ,K + -ATPase field is that the affinity of the E1 conformation appears to differ depending on whether it is measured by an equilibrium method or a presteady-state kinetic method. From ATP binding studies, a single ATP binding equilibrium with a K d in the range 0.12-0.63 µM has been detected (23-27). In contrast, from presteady-state kinetic studies based on enzyme phosphorylation, much higher dissoci...

show abstract

Section: Discussionsupporting

confidence: 91%

Section: Binding Of Mgsupporting

confidence: 72%

ATP Binding Equilibria of the Na⁺,K⁺-ATPase

et al. 2008

View full text Add to dashboard Cite

show abstract

“…Notably, when temperature was raised inhibition disappeared, in agreement with the fact that viscosity decreases when temperature increases (Table 1). Similar results have been obtained with Na + /K + -ATPase and Na + -ATPase in the presence of polyethylene glycol and glycerol (Esmann et al, 2008). In glucose oxidase, activity inhibition by varying concentrations of trehalose was due to the promotion of a highly compact state, which correlated with the increased viscosity of the medium (Paz-Alfaro et al, 2009 Fig.…”

Section: Inhibition Of Isolated Enzymes; Possible Role Of Viscositysupporting

confidence: 82%

Metabolic Optimization by Enzyme-Enzyme and Enzyme-Cytoskeleton Associations

Araiza‐Olivera¹,

Uribe‐Carvajal²,

Chiquete-Félix³

et al. 2012

Cell Metabolism - Cell Homeostasis and Stress Response

View full text Add to dashboard Cite

“…9A), but had no effect on K ϩ -pNPPase (see also Ref. 47). Sucrose and polyethylene glycol 6000 (PEG 6000), at the same concentrations described in Fig.…”

Section: ⅐2kmentioning

confidence: 87%