Superoxide radical formation by pure complex I (NADH:ubiquinone oxidoreductase) from Yarrowia lipolytica.
Generation of reactive oxygen species (ROS) is increasingly recognized as an important cellular process involved in numerous physiological and pathophysiological processes. Complex I (NADH:ubiquinone oxidoreductase) is considered as one of the major sources of ROS within mitochondria. Yet, the exact site and mechanism of superoxide production by this large membrane-bound multiprotein complex has remained controversial. Here we show that isolated complex I from Yarrowia lipolytica forms superoxide at a rate of 0.15% of the rate measured for catalytic turnover. Superoxide production is not inhibited by ubiquinone analogous inhibitors. Because mutant complex I lacking a detectable iron-sulfur cluster N2 exhibited the same rate of ROS production, this terminal redox center could be excluded as a source of electrons. From the effect of different ubiquinone derivatives and pH on this side reaction of complex I we concluded that oxygen accepts electrons from FMNH2 or FMN semiquinone either directly or via more hydrophilic ubiquinone derivatives.
Galkin
Alexander
A
Universität Frankfurt, Fachbereich Medizin, Zentrum der Biologischen Chemie, D-60590 Frankfurt am Main, Germany.
Brandt
Ulrich
U
D002384:Catalysis; D004305:Dose-Response Relationship, Drug; D042967:Electron Transport Complex I / Q000378:metabolism*; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D008928:Mitochondria / Q000378:metabolism; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D017354:Point Mutation; D011510:Proteolipids / Q000378:metabolism; D011809:Quinones / Q000737:chemistry; D017382:Reactive Oxygen Species; D013481:Superoxides / Q000378:metabolism*; D014451:Ubiquinone / Q000378:metabolism; D025062:Yarrowia / Q000201:enzymology / Q000378:metabolism*
D011510:Proteolipids; D011809:Quinones; D017382:Reactive Oxygen Species; C020485:proteoliposomes; D009243:NAD; D013481:Superoxides; D014451:Ubiquinone; D042967:Electron Transport Complex I; D010100:Oxygen