Temperature-dependencies of various catalytic activities of membrane-bound Na+/K+-ATPase from ox brain, ox kidney and shark rectal gland and of C12E8-solubilized shark Na+/K+-ATPase.
The temperature dependence of ouabain-sensitive ATPase and phosphatase activities of membrane fragments containing the Na+/K+-ATPase were investigated in tissue from ox kidney, ox brain and from shark rectal glands. The shark enzyme was also tested in solubilized form. Arrhenius plots of the Na+/K+-ATPase activity seem to be linear up to about 20 degrees C, and non-linear above this temperature. The Arrhenius plots of mammalian enzyme (ox brain and kidney) were steeper, especially at temperatures below 20-30 degrees C, than that of shark enzyme. The Na+-ATPase activity showed a weaker temperature-dependence than the Na+/K+-ATPase activity. The phosphatase reactions measured, K+-stimulated, Na+/K+-stimulated and Na+/K+/ATP-stimulated, also showed a weaker temperature-dependence than the overall Na+/K+-ATPase activity. Among the phosphatase reactions, the largest change in slope of the Arrhenius plot was observed with the Na+/K+/ATP)-stimulated phosphatase reaction. The Arrhenius plots of the partial reactions were all non-linear. Solubilization of shark enzyme in C12E8 did not change the curvature of Arrhenius plots of the Na+/K+-ATPase activity or the K+-phosphatase activity. Since solubilization involves a disruption of the membrane and an 80% delipidation, the observed curvature of the Arrhenius plot can not be attributed to a property of the membrane as such.
Esmann
M
M
Institute of Biophysics, University of Aarhus, Denmark.
Skou
J C
JC
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology*; D003902:Detergents; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D011092:Polyethylene Glycols; D011487:Protein Conformation; D012491:Salt Gland / Q000201:enzymology*; D012754:Sharks; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D012995:Solubility; D013696:Temperature
D003902:Detergents; C017272:dodecyloctaethyleneglycol monoether; D011092:Polyethylene Glycols; D000254:Sodium-Potassium-Exchanging ATPase