Ligand and lipid domain stabilization of a membraneous Ca2+-ATPase during hyperthermia.
The susceptibility of the membranous Ca2+-ATPase of sarcoplasmic reticulum to enzymatic inactivation at hyperthermic temperatures was investigated. Inactivation produced a break in the Arrhenius plot at 45-46 degrees C and was accompanied by an increased mobility of spin label, covalently attached to the Ca2+-ATPase. MgADP and MgATP exerted a markedly stabilizing effect on inactivation, both at pH 7.0 and in acidic media. By contrast, high-affinity Ca2+ or Mg2+ binding only moderately stabilized Ca2+-ATPase (inactivation rates were decreased 2-3 times), and this effect was non-additive, i.e., only observed in the absence of the other divalent cation. But withdrawal of K+ and Na+ gave rise to a pronounced destabilization that could be reversed efficiently by high concentrations of Ca2+ or Mg2+. These results are compared with a previous study on detergent solubilized Ca2+-ATPase (Møller, J.V., Lind, K.E. and Andersen, J.P. (1980) J. Biol. Chem. 255, 1912-1920) which showed the enzyme to be markedly stabilized by Ca2+ as well as by nucleotide. It is concluded that, due to the presence of nucleotide, inactivation of Ca2+-ATPase is not likely to occur during malignant hyperthermia and that the native environment of the lipid bilayer provides stabilization of the membrane-embedded and Ca2+-translocating domain of the Ca2+-ATPase.
Palecz
D
D
Institute of Biochemistry and Biophysics, University of Lodz, Poland.
Grzelinska
E
E
Bartosz
G
G
Leyko
W
W
Møller
J V
JV
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005334:Fever / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008051:Lipid Bilayers; D008274:Magnesium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012964:Sodium / Q000378:metabolism
D008024:Ligands; D008051:Lipid Bilayers; D012964:Sodium; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D011188:Potassium; D002118:Calcium