Open AccessReduction of ubiquinone by lipoamide dehydrogenase
Author(s) -
Xia Ling,
Björnstedt Mikael,
Nordman Tomas,
Eriksson Lennart C.,
Olsson Jerker M.
Publication year - 2001
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2001.02013.x
Subject(s) - chemistry , cofactor , ubiquinol , dehydrogenase , redox , flavin group , divalent , enzyme , biochemistry , inorganic chemistry , coenzyme q – cytochrome c reductase , mitochondrion , organic chemistry , cytochrome c
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 m m and was even further increased at 0.5 m m . 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.