Lobyshev V I, Fogel' Iu, Iakovenko L V, Rezaeva M N, Tverdislov V A
Biofizika. 1982 Jul-Aug;27(4):595-603.
Effect of heavy water D2O on the rate of hydrolysis of ATP and pNPP by Na,K-ATPase was studied. Heavy water of high concentration inhibits the rate of ATPase reaction in all the studied ratios of the ions Na/K at constant ionic strength 150 mM. Activation of the enzyme was observed in the solution with low concentration of heavy water (less than 5%). The value of isotope effects depended on the ratio between sodium and potassium ion concentrations in the medium. At low temperature no activation of the enzyme with heavy water in low concentration was observed. Substitution of usual water for the heavy one was accompanied by a decrease of apparent constants of enzyme activation with sodium and potassium ions. During pNPP hydrolysis with Na,K-ATPase an increase of reaction rate in the medium with heavy water was observed. Substitution of potassium ions by cesium resulted in an increase of isotope effects during ATP and pNPP hydrolysis. Analysis of isotope effects in terms of the molecular model of sodium pump proposed permits a conclusion that the isotope effects of heavy water are explained by its influence as a solvent, the binding centres of potassium and sodium ions are localized in different regions of the enzyme differing in physico-chemical properties. The structure of sodium centres is controlled by hydrogen bonds, and of potassium ones--by hydrophobic interactions; the transport of ions by the enzyme is accompanied by dehydration of ions.
研究了重水D2O对Na，K - ATP酶水解ATP和对硝基苯磷酸酯（pNPP）速率的影响。在恒定离子强度150 mM下，高浓度重水在所有研究的Na/K离子比例中均抑制ATP酶反应速率。在低浓度重水（小于5%）的溶液中观察到酶的激活。同位素效应的值取决于介质中钠离子和钾离子浓度的比例。在低温下，未观察到低浓度重水对酶的激活作用。用重水替代普通水伴随着酶对钠离子和钾离子激活的表观常数降低。在用Na，K - ATP酶水解pNPP过程中，观察到重水介质中反应速率增加。用铯离子替代钾离子导致ATP和pNPP水解过程中同位素效应增加。根据所提出的钠泵分子模型对同位素效应进行分析得出结论，重水的同位素效应可由其作为溶剂的影响来解释，钾离子和钠离子的结合中心位于酶的不同区域，这些区域的物理化学性质不同。钠中心的结构由氢键控制，钾中心的结构由疏水相互作用控制；酶对离子的转运伴随着离子的脱水作用。
