The bulk of Ca2+ released to the myoplasm is free in the sarcoplasmic reticulum and does not unbind from calsequestrin

FEBS Letters

Simon, Bruce J.¹  Volpe, Pompco¹ 

[1] Department of Physiology and Biophysics, The University of Texas Medical Branch, Galveston, TX 77350, USA

关键词: Skeletal muscle;    Ca2+;    Calsequestrin;    Ca2+ release;    Sarcoplasmic reticulum;   

DOI  :  10.1016/0014-5793(91)80134-O

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Calsequestrin (CS) is the major Ca²⁺ binding protein contained in the lumen of sarcoplasmic reticulum (SR). Ca²⁺ binding properties and tissue concentration of CS of frog skeletal muscle were measured. At equilibrium, maximal Ca²⁺ binding capacity of purified CS was about 1.2 μmol Ca²⁺/mg protein. Apparent K _as for Ca²⁺ 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 ⁴⁵Ca 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 [Ca²⁺] of SR was calculated to be 3.6 mM, and, thus, CS is largely saturated with Ca²⁺. Moreover, computer simulations of Ca²⁺ release indicated that about 75% of Ca²⁺ released during a twitch is free in the SR and does not unbind from CS.

【 授权许可】

Unknown