Varma S D, Shen X, Lohman W
Department of Ophthalmology, University of Maryland School of Medicine and Dentistry, Baltimore 21201.
Lens Eye Toxic Res. 1990;7(1):49-66.
Cu-catalyzed oxidation of ascorbate has been studied in the absence and the presence of superoxide dismutase, catalase, mannitol, glycerol, ethanol, formate, and thiourea. None of these agents except thiourea inhibited the reaction. Therefore, the role of the Haber-Weiss reaction in the ascorbate oxidation could not be demonstrated. Electron spin resonance studies demonstrated that the preventive effect of the thiol is primarily due to the chelation of the reduced copper ions with the sulphur atom. The oxidation was also prevented by the chelation of copper with physiological levels of bovine serum albumin. These observations are consistent with the concept that a metal-oxygen complex is perhaps directly involved in the oxidative process. Measurements of the peroxide produced during oxidation indicated that significant amounts of this compound accumulates only at lower levels of ascorbate and in the absence of a protein or other chelating agents. At higher ascorbate levels no peroxide accumulation takes place. These results are, thus, useful in predicting the conditions under which the nutrient may act as a pro-oxidant or as an anti-oxidant. The observations suggest that under normal conditions low levels of ascorbate may act as a pro-oxidant through H2O2 production if the system has transition metal ions devoid of chelating agents. At higher concentrations ascorbate acts predominantly as an antioxidant.
已在不存在和存在超氧化物歧化酶、过氧化氢酶、甘露醇、甘油、乙醇、甲酸盐和硫脲的情况下研究了铜催化的抗坏血酸氧化反应。除硫脲外，这些试剂均未抑制该反应。因此，无法证明哈伯-维伊斯反应在抗坏血酸氧化中的作用。电子自旋共振研究表明，硫醇的预防作用主要是由于还原态铜离子与硫原子的螯合。铜与生理水平的牛血清白蛋白螯合也可防止氧化。这些观察结果与金属-氧络合物可能直接参与氧化过程的概念一致。氧化过程中产生的过氧化物的测量表明，只有在抗坏血酸水平较低且不存在蛋白质或其他螯合剂的情况下，才会积累大量这种化合物。在抗坏血酸水平较高时，不会发生过氧化物积累。因此，这些结果有助于预测该营养素作为促氧化剂或抗氧化剂发挥作用的条件。这些观察结果表明，在正常情况下，如果系统中有缺乏螯合剂的过渡金属离子，低水平的抗坏血酸可能通过产生过氧化氢而作为促氧化剂。在较高浓度下，抗坏血酸主要作为抗氧化剂起作用。
