Petrat Frank, Bramey Thorsten, Kirsch Michael, Kerkweg Uta, De Groot Herbert
Institut für Physiologische Chemie, Universitätsklinikum, Hufelandstr. 55, D-45122, Essen, Germany.
Free Radic Res. 2006 Aug;40(8):857-63. doi: 10.1080/10715760600744795.
Recently we demonstrated that lactate dehydrogenase (LDH)-bound NADH is oxidized by O2, H2O2, HNO2 and peroxynitrite predominantly via a chain radical mechanism which is propagated by superoxide. Here we studied both whether other dehydrogenases also increase their coenzymes' reactivity towards these oxidants and whether a chain radical mechanism is operating. Almost all dehydrogenases increased the oxidation of their physiological coenzymes by at least one of the oxidants. The oxidation of NADH or NADPH depended both on the binding dehydrogenase and the applied oxidant and in some cases the reactions were remarkably fast. The highest rate constant (k = 370 M-1 s-1) was found for the reaction of HNO2 with NADH bound to alcohol dehydrogenase. Regardless of the applied oxidant, superoxide dismutase failed to inhibit the oxidation of protein-bound NADH and NADPH. We therefore conclude that several dehydrogenases increase the oxidation of NADH and/or NADPH by the employed set of oxidants in bimolecular reactions, but, unlike LDH, do not mediate a O2*(-) dependent chain radical mechanism.
最近我们证明，与乳酸脱氢酶（LDH）结合的NADH主要通过由超氧化物传播的链式自由基机制被O2、H2O2、HNO2和过氧亚硝酸盐氧化。在此，我们研究了其他脱氢酶是否也会提高其辅酶对这些氧化剂的反应活性，以及链式自由基机制是否起作用。几乎所有脱氢酶都会使它们的生理性辅酶被至少一种氧化剂氧化的程度增加。NADH或NADPH的氧化既取决于结合的脱氢酶，也取决于所使用的氧化剂，在某些情况下反应非常迅速。HNO2与结合在乙醇脱氢酶上的NADH反应的速率常数最高（k = 370 M-1 s-1）。无论使用何种氧化剂，超氧化物歧化酶都无法抑制蛋白质结合的NADH和NADPH的氧化。因此，我们得出结论，几种脱氢酶在双分子反应中会提高所使用的一组氧化剂对NADH和/或NADPH的氧化程度，但与LDH不同的是，它们不会介导依赖O2*(-)的链式自由基机制。
