Thermal unfolding of monomeric Ca(II), Mg(II)-ATPase from sarcoplasmic reticulum of rabbit skeletal muscle.
The thermal unfolding of monomeric and delipidated Ca(2+)-ATPase, solubilized in C12E8, can be appropriately described as a non-two-state irreversible denaturation, with only one endothermic peak. In the Ca2+ concentration range (0-0.5 mM) which stimulates the ATPase activity of solubilized monomeric ATPase, Ca2+ shifts the critical temperature midpoint of the denaturation process (Tm) from 42 to 50 degrees C without segregation of the endothermic peak into two separate components. Because 20 mM Mg2+ only shifts the Tm from 42 to 44 degrees C, we conclude that the effect of Ca2+ upon the Tm is likely to be due to binding to the high affinity Ca2+ sites in the ATPase. The effect of Ca2+ upon the enthalpy of denaturation is biphasic, suggesting the presence of low affinity Ca2+ sites (K0.5 in the millimolar range) in monomeric and solubilized ATPase.
Merino
J M
JM
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.
Moller
J V
JV
Gutiérrez-Merino
C
C
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000737:chemistry*; D004795:Enzyme Stability; D017510:Protein Folding; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012995:Solubility; D013053:Spectrophotometry; D013816:Thermodynamics
D017301:Ca(2+) Mg(2+)-ATPase