title: Brain (Na+,K+)-ATPase. Opposite effects of ethanol and dimethyl sulfoxide on temperature dependence of enzyme conformation and univalent cation binding.
abstract: We examined effects of ethanol and dimethyl sulfoxide on the regulation and apparent thermodynamic properties of moderate affinity Na+ and K+ binding that regulates the K+-dependent phosphatase activity of (Na+,K+)-ATPase. Ethanol and other alcohols reduced the apparent affinity for Na+ and K+ at their moderate affinity sites and increased the negative delta H and delta S of cation binding. Dimethyl sulfoxide had the opposite effects. Inhibition by ethanol was favored by high temperature or low K+. Ethanol potentiated inhibition of K+ binding by ATP or Mg2+. Ethanol also shifted the equilibrium between K+-sensitive and -insensitive forms of (Na+,K+)-ATPase toward the K+-sensitive form; in this case, it reduced the negative delta H and delta S for the transition to K+-sensitive enzyme. Again, dimethyl sulfoxide had the opposite effects. These data indicate that ethanol and other agents considered to affect membrane fluidity act by a combination of membrane (on cation binding) and solvent (on conformation) effects. The most important effect of ethanol and similar agents on the enzyme is to prevent the formation of K+-sensitive enzyme by cation binding and to destabilize K+-sensitive enzyme in the presence of ATP. These results also add further evidence that the sites by which Na+ and K+ produce K+-sensitive enzyme are similar or identical.
mesh_terms: D000438:Alcohols / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002414:Cations, Monovalent; D002417:Cattle; D004121:Dimethyl Sulfoxide / Q000494:pharmacology*; D000431:Ethanol / Q000494:pharmacology*; D007700:Kinetics; D008024:Ligands; D011487:Protein Conformation / Q000187:drug effects; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013696:Temperature
chemical_list: D000438:Alcohols; D002414:Cations, Monovalent; D008024:Ligands; D000431:Ethanol; D000254:Sodium-Potassium-Exchanging ATPase; D004121:Dimethyl Sulfoxide