Maier K L, Hinze H, Meyer B, Lenz A G
GSF--National Research Center for Environment and Health, Institute of Inhalation Biology, Neuherberg, Germany.
FEBS Lett. 1996 Oct 28;396(1):95-8. doi: 10.1016/0014-5793(96)01054-x.
The role of thiols as oxidant scavengers during inactivation of bovine glucose-6-phosphate dehydrogenase by metal-catalyzed oxidation systems has been studied in vitro. Partial inactivation of the enzyme was achieved by the metal-catalyzed oxidation systems Fe(II)/H202/EDTA or Fe(II)/H202/ADP under specific conditions. When EDTA as chelator was present in the oxidation system, both cysteine and N-acetylcysteine at low concentrations (0.1-1 mM) drastically enhanced inactivation, while cysteinyl-glycine and glutathione did not. The thiol-mediated inactivation was inhibitable by superoxide dismutase. Depletion of enzyme activity by cysteine was paralleled by an increase of the carbonyl content, which indicates oxidative injury. However, when EDTA as chelator was replaced by the natural chelator ADP, all thiols studied acted as antioxidants. It is therefore concluded that the nature of the chelator as a constituent of the metal-catalyzed oxidation systems determines whether the antioxidative function of some thiols is shifted to a prooxidative function against glucose-6-phosphate dehydrogenase.
已在体外研究了硫醇在金属催化氧化体系使牛葡萄糖-6-磷酸脱氢酶失活过程中作为氧化剂清除剂的作用。在特定条件下，金属催化氧化体系Fe(II)/H₂O₂/EDTA或Fe(II)/H₂O₂/ADP可使该酶部分失活。当氧化体系中存在作为螯合剂的EDTA时，低浓度（0.1 - 1 mM）的半胱氨酸和N-乙酰半胱氨酸都会显著增强失活作用，而半胱氨酰甘氨酸和谷胱甘肽则不会。硫醇介导的失活作用可被超氧化物歧化酶抑制。半胱氨酸导致的酶活性消耗与羰基含量增加同时出现，这表明存在氧化损伤。然而，当作为螯合剂的EDTA被天然螯合剂ADP取代时，所研究的所有硫醇都起到抗氧化剂的作用。因此可以得出结论，作为金属催化氧化体系组成成分的螯合剂的性质决定了某些硫醇的抗氧化功能是否会转变为针对葡萄糖-6-磷酸脱氢酶的促氧化功能。
