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Thermal unfolding of monomeric Ca(II),Mg(II)‐ATPase from sarcoplasmic reticulum of rabbit skeletal muscle
Author(s) -
Merino Jaime M.,
Moller Jesper V.,
Gutiérrez-Merino Carlos
Publication year - 1994
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(94)80309-9
Subject(s) - chemistry , endothermic process , monomer , denaturation (fissile materials) , atpase , calcium atpase , endoplasmic reticulum , enthalpy , crystallography , solubilization , mole , biophysics , stereochemistry , biochemistry , enzyme , nuclear chemistry , thermodynamics , biology , organic chemistry , physics , adsorption , polymer
The thermal unfolding of monomeric and delipidated Ca 2+ ‐ATPase, solubilized in C 12 E 8 , can be appropriately described as a non‐two‐state irreversible denaturation, with only one endothermic peak. In the Ca 2+ concentration range (0–0.5 mM) which stimulates the ATPase activity of solubilized monomeric ATPase, Ca 2+ shifts the critical temperature midpoint of the denaturation process ( T m ) from 42 to 50°C without segregation of the endothermic peak into two separate components. Because 20 mM Mg 2+ only shifts the T m from 42 to 44°C, we conclude that the effect of Ca 2+ upon the T m is likely to be due to binding to the high affinity Ca 2+ sites in the ATPase. The effect of Ca 2+ upon the enthalpy of denaturation is biphasic, suggesting the presence of low affinity Ca 2+ sites ( K 0.5 in the millimolar range) in monomeric and solubilized ATPase.