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.

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.

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 Mutation of the high affinity calcium binding sites in cardiac troponin C.

1992 ◽  
Vol 267 (2) ◽  
pp. 825-831 ◽  
Author(s):  
J C Negele ◽  
D G Dotson ◽  
W Liu ◽  
H L Sweeney ◽  
J A Putkey
Keyword(s):  
Binding Sites ◽  
Calcium Binding ◽  
Cardiac Troponin ◽  
Troponin C ◽  
High Affinity ◽  
Cardiac Troponin C ◽  
Calcium Binding Sites

Rat GTP cyclohydrolase I is a homodecameric protein complex containing high-affinity calcium-binding sites 1 1Edited by W. Baumeister

1998 ◽  
Vol 279 (1) ◽  
pp. 189-199 ◽  
Author(s):  
Michel O Steinmetz ◽  
Christoph Plüss ◽  
Urs Christen ◽  
Bettina Wolpensinger ◽  
Ariel Lustig ◽  
...  
Keyword(s):  
Protein Complex ◽  
Binding Sites ◽  
Calcium Binding ◽  
Gtp Cyclohydrolase I ◽  
Gtp Cyclohydrolase ◽  
High Affinity ◽  
Calcium Binding Sites

scholarly journals Characterization of the calcium-binding sites of calcineurin B

FEBS Letters ◽  
1995 ◽  
Vol 362 (1) ◽  
pp. 55-58 ◽  
Author(s):  
Lazaros T Kakalis ◽  
Michael Kennedy ◽  
Robert Sikkink ◽  
Frank Rusnak ◽  
Ian M Armitage
Keyword(s):  
Binding Sites ◽  
Calcium Binding ◽  
Calcineurin B ◽  
Calcium Binding Sites

scholarly journals Conformational epitopes at cadherin calcium-binding sites and p120-catenin phosphorylation regulate cell adhesion

2012 ◽  
Vol 23 (11) ◽  
pp. 2092-2108 ◽  
Author(s):  
Yuliya I. Petrova ◽  
MarthaJoy M. Spano ◽  
Barry M. Gumbiner
Keyword(s):  
Cell Surface ◽  
Conformational Changes ◽  
Binding Sites ◽  
Calcium Binding ◽  
Cell Types ◽  
P120 Catenin ◽  
Physiological Regulation ◽  
Conformational Epitopes ◽  
Calcium Binding Sites ◽  
E Cadherin

We investigated changes in cadherin structure at the cell surface that regulate its adhesive activity. Colo 205 cells are nonadhesive cells with a full but inactive complement of E-cadherin–catenin complexes at the cell surface, but they can be triggered to adhere and form monolayers. We were able to distinguish the inactive and active states of E-cadherin at the cell surface by using a special set of monoclonal antibodies (mAbs). Another set of mAbs binds E-cadherin and strongly activates adhesion. In other epithelial cell types these activating mAbs inhibit growth factor–induced down-regulation of adhesion and epithelial morphogenesis, indicating that these phenomena are also controlled by E-cadherin activity at the cell surface. Both types of mAbs recognize conformational epitopes at different interfaces between extracellular cadherin repeat domains (ECs), especially near calcium-binding sites. Activation also induces p120-catenin dephosphorylation, as well as changes in the cadherin cytoplasmic domain. Moreover, phospho-site mutations indicate that dephosphorylation of specific Ser/Thr residues in the N-terminal domain of p120-catenin mediate adhesion activation. Thus physiological regulation of the adhesive state of E-cadherin involves physical and/or conformational changes in the EC interface regions of the ectodomain at the cell surface that are mediated by catenin-associated changes across the membrane.

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