title: Effects of deuterium oxide on elementary steps in the ATPase reaction. Evidence for the similarity of key intermediates in contractile and transport ATPase.
abstract: The effects of D2O on the elementary steps in the contractile and transport ATPase [EC 3.6.1.3] reactions were studied, and the following results were obtained: 1. The rate of H-meromyosin ATPase in the steady state decreased in D2O to 60% of that in H2O. Deuterium oxide did not affect the size or rate of the initial burst of Pi liberation, i.e. the amount or rate of formation of the reactive myosin-phosphate-ADP complex, MADPP. Moreover, neither the rate of change in the fluorescence spectrum of H-meromyosin induced by ATP (the rate of formation of the second enzyme-ATP complex, M2ATP) nor the rate constant of decomposition of MADPP into M degrees + ADP + Pi was affected by D2O. However, the equilibrium constant of the step M2ATP in equilibrium MADPP decreased in D2O to about 1/2 the value in H2O. 2. In the case of the Na+-K+-dependent ATPase reactin, neither the rate constant of formation of the second enzyme-ATP complex, E2ATP, nor that of decomposition of a phosphorylated intermediate, EADP approximately P, was affected by D2O. However, the equilibrium constant of the step E2ATP in equilibrium EADP approximately P decreased in D2O to about 1/2.5-1/4 of the value in H2O. These results suggest a similarity between the modes of binding of phosphate in MADPP in the myosin ATPase reaction and in EADP approximatley P in the Na+-K+-dependent ATPase reaction.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D003903:Deuterium; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008433:Mathematics; D009119:Muscle Contraction; D009132:Muscles / Q000201:enzymology*; D015879:Myosin Subfragments / Q000378:metabolism*; D009928:Organ Specificity; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D012965:Sodium Chloride; D000244:Adenosine Diphosphate; D011189:Potassium Chloride; D003903:Deuterium; D000251:Adenosine Triphosphatases