pH-Induced changes in the reactions controlled by the low- and high-affinity calcium(2+)-binding sites in sarcoplasmic reticulum

Biochemistry ◽  
1977 ◽  
Vol 16 (2) ◽  
pp. 329-334 ◽  
Author(s):  
Sergio Verjovski-Almeida ◽  
Leopoldo De Meis
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
High Affinity ◽  
Induced Changes

scholarly journals A kinetic model for Ca2+ efflux mediated by the Ca2+ + Mg2+-activated ATPase of sarcoplasmic reticulum

1987 ◽  
Vol 245 (3) ◽  
pp. 713-721 ◽  
Author(s):  
J M McWhirter ◽  
G W Gould ◽  
J M East ◽  
A G Lee
Keyword(s):  
Experimental Data ◽  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Kinetic Model ◽  
Atpase Activity ◽  
Binding Site ◽  
Binding Sites ◽  
Adenine Nucleotides ◽  
Contraction Coupling ◽  
High Affinity

We present a model for Ca2+ efflux from vesicles of sarcoplasmic reticulum (SR). It is proposed that efflux is mediated by the Ca2+ + Mg2+-activated ATPase that is responsible for Ca2+ uptake in this system. In the normal ATPase cycle of the ATPase, phosphorylation of the ATPase is followed by a conformational change in which the Ca2+-binding sites change from being outward-facing and of high affinity to being inward-facing and of low affinity. To mediate Ca2+ efflux, it is proposed that the ATPase can adopt a conformation in which the Ca2+-binding sites are of low affinity but still outward-facing. It is shown that experimental data on the rates of Ca2+ efflux can be simulated in terms of this model, with Ca2+-binding-site affinities previously proposed to explain ATPase activity [Gould, East, Froud, McWhirter, Stefanova & Lee (1986) Biochem. J. 237, 217-227]. Effects of Mg2+ and adenine nucleotides on efflux rates are explained. It is suggested that Ca2+ efflux from SR mediated by the ATPase could be important in excitation-contraction coupling in skeletal muscle.

scholarly journals The effects of membrane potential and lanthanides on the conformation of the Ca2+-transport ATPase in sarcoplasmic reticulum

1986 ◽  
Vol 234 (2) ◽  
pp. 363-371 ◽  
Author(s):  
I Jona ◽  
A Martonosi
Keyword(s):  
Membrane Potential ◽  
Sarcoplasmic Reticulum ◽  
Fluorescence Intensity ◽  
Binding Sites ◽  
Fluorescein Isothiocyanate ◽  
Tryptophan Fluorescence ◽  
Lanthanide Ions ◽  
Positive Potential ◽  
High Affinity ◽  
Ion Substitution

The effects of Ca2+, lanthanide ions (Gd3+, La3+ and Pr3+) and membrane potential on the fluorescence of tryptophan and covalently bound fluorescein were analysed in native and fluorescein isothiocyanate (FITC)-labelled sarcoplasmic reticulum vesicles. The binding of Ca2+ and lanthanides to the Ca2+-ATPase increases the fluorescence intensity of tryptophan and decreases the fluorescence intensity of FITC; the dependence of these effects on cation concentration is consistent with the involvement of the high-affinity Ca2+-binding sites of the Ca2+-ATPase in the cation-induced fluorescence changes. The fluorescence of FITC-labelled sarcoplasmic reticulum vesicles is also influenced by membrane potential changes induced by ion substitution. Inside positive potential increases, while inside negative potential decreases, the fluorescence of bound FITC. Smaller potential-dependent changes in tryptophan fluorescence were also observed. The effects of Ca2+, lanthanides and membrane potential on the fluorescence of tryptophan and FITC are discussed in terms of the two major conformations of the Ca2+-ATPase (E1 and E2), that are assumed to alternate during Ca2+ transport. The observations support the suggestion [Dux, Taylor, Ting-Beall & Martonosi (1985) J. Biol. Chem. 260, 11730-11743] that the vanadate-induced crystals of Ca2+-ATPase represent the E2, while the Ca2+ and lanthanide-induced crystals the E1, conformation of the enzyme.

scholarly journals Characterization of ruthenium red-binding sites of the Ca2+-ATPase from sarcoplasmic reticulum and their interaction with Ca2+-binding sites

1992 ◽  
Vol 287 (3) ◽  
pp. 767-774 ◽  
Author(s):  
S Corbalan-Garcia ◽  
J A Teruel ◽  
J C Gomez-Fernandez
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Ruthenium Red ◽  
Cation Binding ◽  
Binding Studies ◽  
High Affinity ◽  
Cation Binding Site ◽  
Kinetics Of ◽  
Fast Release

Sarcoplasmic reticulum Ca(2+)-ATPase has previously been shown to bind and dissociate two Ca2+ ions in a sequential mode. This behaviour is confirmed here by inducing sequential Ca2+ dissociation with Ruthenium Red. Ruthenium Red binds to sarcoplasmic reticulum vesicles (6 nmol/mg) with a Kd = 2 microM, producing biphasic kinetics of Ca2+ dissociation from the Ca(2+)-ATPase, decreasing the affinity for Ca2+ binding. Studies on the effect of Ca2+ on Ruthenium Red binding indicate that Ruthenium Red does not bind to the high-affinity Ca(2+)-binding sites, as suggested by the following observations: (i) micromolar concentrations of Ca2+ do not significantly alter Ruthenium Red binding to the sarcoplasmic reticulum; (ii) quenching of the fluorescence of fluorescein 5′-isothiocyanate (FITC) bound to Ca(2+)-ATPase by Ruthenium Red (resembling Ruthenium Red binding) is not prevented by micromolar concentrations of Ca2+; (iii) quenching of FITC fluorescence by Ca2+ binding to the high-affinity sites is achieved even though Ruthenium Red is bound to the Ca(2+)-ATPase; and (iv) micromolar Ca2+ concentrations prevent inhibition of the ATP-hydrolytic capability by dicyclohexylcarbodi-imide modification, but Ruthenium Red does not. However, micromolar concentrations of lanthanides (La3+ and Tb3+) and millimolar concentrations of bivalent cations (Ca2+ and Mg2+) inhibit Ruthenium Red binding as well as quenching of FITC-labelled Ca(2+)-ATPase fluorescence by Ruthenium Red. Studies of Ruthenium Red binding to tryptic fragments of Ca(2+)-ATPase, as demonstrated by ligand blotting, indicate that Ruthenium Red does not bind to the A1 subfragment. Our observations suggest that Ruthenium Red might bind to a cation-binding site in Ca(2+)-ATPase inducing fast release of the last bound Ca2+ by interactions between the sites.

scholarly journals Dependence on Membrane Lipids of the Effect of Vanadate on Calcium and ATP Binding to Sarcoplasmic Reticulum ATPase

1984 ◽  
Vol 39 (11-12) ◽  
pp. 1137-1140 ◽  
Author(s):  
Pankaj Medda ◽  
Wilhelm Hasselbach
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Calcium Binding ◽  
Membrane Lipids ◽  
Nucleotide Binding ◽  
Atp Binding ◽  
Transport Atpase ◽  
Nucleotide Binding Sites ◽  
High Affinity ◽  
Calcium Binding Sites

Abstract The affinity of the sarcoplasmic reticulum transport ATPase for calcium and ATP is not affected by lipid depriviation while vanadate binding is completely abolished. Lipid substitution restores vanadate binding as well as the vanadate induced disappearance of the enzyme’s high affinity calcium and nucleotide binding sites. Nucleotide binding is simultaneously restored with the displacement of vanadate from the enzyme following the occupation of its low affinity calcium binding sites.

scholarly journals Allosteric Modulation of GPCRs of Class A by Cholesterol

2021 ◽  
Vol 22 (4) ◽  
pp. 1953
Author(s):  
Jan Jakubík ◽  
Esam E. El-Fakahany
Keyword(s):  
Binding Sites ◽  
Allosteric Modulation ◽  
G Protein Coupled Receptors ◽  
Membrane Cholesterol ◽  
Extracellular Signals ◽  
High Affinity ◽  
Class A ◽  
Specific Effects ◽  
Induced Changes ◽  
G Protein Coupled

G-protein coupled receptors (GPCRs) are membrane proteins that convey extracellular signals to the cellular milieu. They represent a target for more than 30% of currently marketed drugs. Here we review the effects of membrane cholesterol on the function of GPCRs of Class A. We review both the specific effects of cholesterol mediated via its direct high-affinity binding to the receptor and non-specific effects mediated by cholesterol-induced changes in the properties of the membrane. Cholesterol binds to many GPCRs at both canonical and non-canonical binding sites. It allosterically affects ligand binding to and activation of GPCRs. Additionally, it changes the oligomerization state of GPCRs. In this review, we consider a perspective of the potential for the development of new therapies that are targeted at manipulating the level of membrane cholesterol or modulating cholesterol binding sites on to GPCRs.

scholarly journals Allosteric Modulation of GPCRs of Class A by Cholesterol

2021 ◽  
Author(s):  
Jan Jakubík ◽  
Esam E. El-Fakahany
Keyword(s):  
Binding Sites ◽  
Allosteric Modulation ◽  
G Protein Coupled Receptors ◽  
Membrane Cholesterol ◽  
Extracellular Signals ◽  
High Affinity ◽  
Class A ◽  
Specific Effects ◽  
Induced Changes ◽  
G Protein Coupled

G-protein coupled receptors (GPCRs) are membrane proteins that convey extracellular signals to the cellular milieu. They represent a target for more than 30 % of currently marketed drugs. Here we review the effects of membrane cholesterol on the function of GPCRs of Class A. We review both the specific effects of cholesterol mediated via its direct high-affinity binding to the receptor and non-specific effects mediated by cholesterol-induced changes in the properties of the membrane. Cholesterol binds to many GPCRs at both canonical and non-canonical binding sites. It allosterically affects ligand binding to and activation of GPCRs. Also, it changes the oligomerization state of GPCRs. In this review, we consider a perspective of the potential for the development of new therapies that are targeted at manipulating the level of membrane cholesterol or modulating cholesterol binding sites on to GPCRs.

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