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The bulk of Ca 2+ released to the myoplasm is free in the sarcoplasmic reticulum and does not unbind from calsequestrin
Author(s) -
Volpe Pompco,
Simon Bruce J.
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)80134-o
Subject(s) - calsequestrin , endoplasmic reticulum , chemistry , biophysics , calcium , skeletal muscle , analytical chemistry (journal) , biochemistry , chromatography , ryanodine receptor , anatomy , biology , organic chemistry
Calsequestrin (CS) is the major Ca 2+ binding protein contained in the lumen of sarcoplasmic reticulum (SR). Ca 2+ binding properties and tissue concentration of CS of frog skeletal muscle were measured. At equilibrium, maximal Ca 2+ binding capacity of purified CS was about 1.2 μmol Ca 2+ /mg protein. Apparent K a s for Ca 2+ were around 50 μM in the absence of salts, around 0.9 mM in the presence of 100 mM KCl, and around 1.1 mM under ‘physiological’ conditions. Quantitation of CS in homogenates was accomplished by three methods (Stains‐all staining, immunobiolting and 45 Ca ligand overlay). Frog muscle contained about 0.5 mg of CS/g wet weight, that is 6.1 mM CS inside the SR. At rest the in situ free [Ca 2+ ] of SR was calculated to be 3.6 mM, and, thus, CS is largely saturated with Ca 2+ . Moreover, computer simulations of Ca 2+ release indicated that about 75% of Ca 2+ released during a twitch is free in the SR and does not unbind from CS.