Low Affinity Calcium Binding Sites of the Calcium Transport ATPase of Sarcoplasmic Reticulum Membranes

1980 ◽  
Vol 35 (11-12) ◽  
pp. 1012-1018 ◽  
Author(s):  
Wilhelm Hasselbach ◽  
Vera Koenig
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Calcium Binding ◽  
Calcium Transport ◽  
External Surface ◽  
Transport Atpase ◽  
Affinity Constants ◽  
Calcium Binding Sites ◽  
Short Time

Calcium binding sites having low affinity constants of < 103 ᴍ-1 were titrated in native sarcoplasmic reticulum vesicles as well as in lipid deprived membranes and in the isolated calcium transport ATPase. Short time calcium binding measurements and the determination of the calcium binding heat allow to distinguish low affinity calcium binding sites located on the external surface of the sarcoplasmic reticulum membranes from those present in the section of the transport molecule directed to the vesicular space. The same number of internal binding sites was found for preparations deprived of their lipid content as well as of preparations depleted of their lipids and of their accessorial proteins. Magnesium interferes with calcium binding to the external as well as to the internal low affinity calcium binding sites. The implications of the existence of the low affinity calcium binding sites in the internal section of the calcium transport ATPase are discussed.

A Conformational Transition of the Sarcoplasmic Reticulum Calcium Transport ATPase Induced by Vanadate

1983 ◽  
Vol 38 (11-12) ◽  
pp. 1015-1022 ◽  
Author(s):  
Wilhelm Hasselbach ◽  
Pankaj Medda ◽  
Andrea Migala ◽  
Bruno Agostini
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Calcium Binding ◽  
Calcium Transport ◽  
Conformational Transition ◽  
Transport Atpase ◽  
Calcium Binding Sites ◽  
Protein Particles ◽  
Sarcoplasmic Reticulum Calcium ◽  
Internal Calcium

Vanadate binding to sarcoplasmic reticulum vesicles results in the loss of the externally located high affinity calcium binding sites of the calcium transport ATPase. Conversely the occupation by calcium of the internally located low affinity sites in the vanadate enzyme complex leads to the release of vanadate. Since the total number of calcium binding sites is not diminished by vanadate binding but slightly increases we conclude that vanadate binding induces a transition of the enzymes external high to internal low affinity calcium binding sites. The transposition of external to internal calcium binding sites is accompanied by a definite change in the structure of the sarcoplasmic reticulum membranes. On vanadate binding the asymmetrically arranged electron dense protein particles become symmetrically distributed

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 Intracellular Calcium Binding and Release in Frog Heart

1973 ◽  
Vol 62 (6) ◽  
pp. 693-706 ◽  
Author(s):  
Saul Winegrad
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Intracellular Calcium ◽  
Binding Sites ◽  
Calcium Binding ◽  
Calcium Content ◽  
Frog Heart ◽  
Affinity Constant ◽  
Total Calcium ◽  
Abrupt Changes ◽  
Calcium Binding Sites

The capacities and affinities of intracellular calcium-binding sites have been studied in frog ventricles, in which the concentration of Ca++ in the sarcoplasm can be controlled as a result of treatment with EDTA. The total calcium content of calcium-depleted and nondepleted muscles at rest and muscles generating considerable tension was 0.8, 1.4, and 5.4 µmol/g of muscle, respectively. Net movement of calcium into or out of the cells occurred without change in tension when the sarcoplasmic concentration of Ca++ was either of two values, less than 10-7 M or approximately 5 x 10-7 M. These data can be explained by the presence of two groups of intracellular calcium sinks which compete with the contractile proteins, one with a capacity of about 0.6 µmol/g and an affinity constant greater than 107 M-1 and a second with a capacity of 4.0 µmol/g and an affinity constant of about 2 x 106 M-1. The higher affinity calcium is released by anoxia, oligomycin, or abrupt changes in sarcoplasmic Ca++. Muscles soaked in Sr-Ringer's contain electron densities in the sarcoplasmic reticulum and to a lesser extent in the mitochondria.

scholarly journals The Site of Calcium Binding in Relation to the Activation of Myofibrillar Contraction

1968 ◽  
Vol 51 (5) ◽  
pp. 655-676 ◽  
Author(s):  
Franklin Fuchs ◽  
F. Norman Briggs
Keyword(s):  
G Protein ◽  
Binding Sites ◽  
Calcium Binding ◽  
Protein Extraction ◽  
Affinity Constant ◽  
Free Calcium ◽  
Apparent Affinity ◽  
Affinity Constants ◽  
Class 1 ◽  
Calcium Binding Sites

Skeletal muscle myofibrils, in the presence of 2 mM MgCl2 at pH 7.0, were found to have two classes of calcium-binding sites with apparent affinity constants of 2.1 x 106 M-1 (class 1) and ∼3 x 104 M-1 (class 2), respectively. At free calcium concentrations essential for the activation of myofibrillar contraction (∼10-6 M) there would be significant calcium binding only to the class 1 sites. These sites could bind about 1.3 µmoles of calcium per g protein. Extraction of myosin from the myofibrils did not alter their calcium-binding parameters. Myosin A, under identical experimental conditions, had little affinity for calcium. The class 1 sites are, therefore, presumed to be located in the I filaments. The class 1 sites could only be detected in F actin and myosin B preparations which were contaminated with the tropomyosin-troponin complex. Tropomyosin bound very little calcium. Troponin, which in conjunction with tropomyosin confers calcium sensitivity on actomyosin systems, could bind 22 µmoles of calcium per g protein with an apparent affinity constant of 2.4 x 106 M-1. In view of the identical affinity constants of the myofibrils and troponin and the much greater number of calcium-binding sites on troponin it is suggested that calcium activates myofibrillar contraction by binding to the troponin molecule.

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