title: The effect of Na+ and K+ on the thermal denaturation of Na+ and + K+-dependent ATPase.
abstract: To increase our understanding of the physical nature of the Na+ and K+ forms of the Na+ + K+-dependent ATPase, thermal-denaturation studies were conducted in different types of ionic media. Thermal-denaturation measurements were performed by measuring the regeneration of ATPase activity after slow pulse exposure to elevated temperatures. Two types of experiments were performed. First, the dependence of the thermal-denaturation rate on Na+ and K+ concentrations was examined. It was found that both cations stabilized the pump protein. Also, K+ was a more effective stabilizer of the native state than was Na+. Secondly, a set of thermodynamic parameters was obtained by measuring the temperature-dependence of the thermal-denaturation rate under three ionic conditions: 60 mM-K+, 150 mM-Na+ and no Na+ or K+. It was found that ion-mediated stabilization of the pump protein was accompanied by substantial increases in activation enthalpy and entropy, the net effect being a less-pronounced increase in activation free energy.
mesh_terms: D000818:Animals; D006358:Hot Temperature; D011188:Potassium / Q000494:pharmacology*; D011489:Protein Denaturation / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine; D013816:Thermodynamics
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium