title: Effects of deuterium on the kinetics of beef heart mitochondrial ATPase.
abstract: A study was done examining the steady-state kinetics of F1-catalyzed ATP and ITP hydrolyses in the presence or absence of D2O as a function of temperature. The steady-state kinetic parameters kcat and kcat/Km were obtained. For ATP hydrolysis, kcat/Km was independent of temperature in the presence or absence of D2O, while kcat/Km for ITP hydrolysis increased in both cases. The relative magnitudes of change of kcat and kcat/Km in the presence and absence of D2O over the temperature range studied were much different for the cases of ATP and ITP hydrolysis. A normal isotope effect was observed in plots of kcat H2O/kcat D2O versus temperature for ATP hydrolysis, which increased then leveled off as temperature increased. An inverse isotope effect at low temperatures changed to a normal isotope effect and increased dramatically as temperature increased during ITP hydrolysis. The results are discussed in terms of the nature and location of the rate-limiting steps in the reaction mechanisms.
mesh_terms: D000818:Animals; D002384:Catalysis; D002417:Cattle; D003903:Deuterium; D017666:Deuterium Oxide; D006868:Hydrolysis; D007293:Inosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D013696:Temperature; D014867:Water
chemical_list: D014867:Water; D007293:Inosine Triphosphate; D003903:Deuterium; D006180:Proton-Translocating ATPases; D017666:Deuterium Oxide