title: An analysis of biphasic time courses: the inactivation of (Na+ + K+)-ATPase and Ca2+-ATPase by ATP-analogs.
abstract: The inactivation of (NA+ + K+)-ATPase and Ca2+-ATPase brought about by the substitution of ATP by covalently binding analogs is studied. Most of the analogs cause biphasic courses of inactivation. The families of time courses obtained for different concentrations of the analog exhibit a characteristic feature that is common to both ATPases. The times of transition from one branch to the other of the biphasic curves are practically independent of the concentration of the analog. An analysis of the eigenvalues from different reaction models shows that for these time evolutions the enzyme exists necessarily in two states, only one of which is active for the analog. As a preliminary attempt, the models have been fitted to the experimental data of three different sets of families of curves. It is demonstrated that a two-sites model of inactivation of (Na+ + K+)-ATPase postulated in the literature cannot be valid.
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives*; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins / Q000494:pharmacology; D007700:Kinetics; D008956:Models, Chemical; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013552:Swine; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D005452:Fluoresceins; D013861:Thiocyanates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D016650:Fluorescein-5-isothiocyanate