title: Radiation inactivation of (Na,K)-ATPase, an enzyme showing multiple radiation-sensitive domains.
abstract: The radiation inactivation of membrane-bound (Na,K)-ATPase from pig kidney was studied by irradiating lyophilized enzyme preparations in vacuo. Various results were obtained depending upon the function assayed. The apparent target size of (Na,K)-ATPase activity was found to be 264 kDa an the high affinity binding sites for ATP, vanadate, and ouabain (bound in the presence of Na+, Mg2+, and ATP) had an apparent target size of 145 kDa. The binding of ouabain in the presence of Mg2+ alone seemed to depend upon the integrity of a domain with a target size of approximately 100 kDa. Na-ATPase and p-nitrophenyl phosphatase, assayed under a variety of conditions, gave inactivation kinetics that did not conform to classical target theory. All the results have been assembled into a model according to which 1) the membrane-bound enzyme is an (alpha beta)2-dimer; 2) there is radiation energy coupling between all four peptides in a molecule, and 3) each alpha-peptide consists of five discrete and independent radiation-sensitive domains with specific functions in the enzymatic reactions catalyzed by the sodium pump.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000528:radiation effects; D001921:Brain / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology; D008433:Mathematics; D010042:Ouabain / Q000378:metabolism; D011487:Protein Conformation; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000528:radiation effects*; D013552:Swine; D014639:Vanadium / Q000378:metabolism
chemical_list: D014639:Vanadium; D010042:Ouabain; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase