Xia L, Björnstedt M, Nordman T, Eriksson L C, Olsson J M
Department of Microbiology, Pathology and Immunology, Division of Pathology, Karolinska Institutet, Huddinge University Hospital, Stockholm, Sweden.
Eur J Biochem. 2001 Mar;268(5):1486-90. doi: 10.1046/j.1432-1327.2001.02013.x.
Lipoamide dehydrogenase belongs to a family of pyridine nucleotide disulfide oxidoreductases and is ubiquitous in aerobic organisms. This enzyme also reduces ubiquinone (the only endogenously synthesized lipid-soluble antioxidant) to ubiquinol, the form in which it functions as an antioxidant. The reduction of ubiquinone was linear with time and exhibited turnover numbers of 5 and 1.2 min(-1) in the presence and absence of zinc, respectively. The reaction was stimulated by zinc and cadmium but not by the other divalent ions tested. The zinc/cadmium-dependent stimulation of the reaction increased rapidly and linearly up to a concentration of 0.1 mM and was even further increased at 0.5 mM. At pH 6, the activity was three times higher than at physiological pH. Alteration of the NADPH : NADP(+) ratio revealed that the reaction is inhibited by higher concentrations of the oxidized cofactors. FAD reduced ubiquinone in a dose-dependent manner at a considerably lower rate, suggesting that the reduction of ubiquinone by lipoamide dehydrogenase involves the FAD moiety of the enzyme.
硫辛酰胺脱氢酶属于吡啶核苷酸二硫化物氧化还原酶家族，在需氧生物中普遍存在。该酶还可将泛醌（唯一内源性合成的脂溶性抗氧化剂）还原为泛醇，泛醇作为抗氧化剂发挥作用。泛醌的还原与时间呈线性关系，在有锌和无锌存在时，其转换数分别为5和1.2 min⁻¹。该反应受锌和镉的刺激，但不受所测试的其他二价离子的刺激。锌/镉对反应的依赖性刺激在浓度达到0.1 mM之前迅速且呈线性增加，在0.5 mM时甚至进一步增加。在pH 6时，活性比生理pH时高三倍。NADPH:NADP⁺比例的改变表明，该反应受到较高浓度氧化辅因子的抑制。FAD以剂量依赖的方式以相当低的速率还原泛醌，这表明硫辛酰胺脱氢酶对泛醌的还原涉及该酶的FAD部分。
