ELECTRON TRANSPORT CHAIN • Complex I: NADH dehydrogenase - aka NADH-CoQ reductase - NADH delivers 2 electrons to the complex I and is oxidized to NAD+ • CoQ (aka Q10 and ubiquinone) - Lipid-soluble - Mobile carrier - NOT a protein • Complex II: succinate dehydrogenase - aka Succinate-CoQ reductase - Also part of citric acid cycle - FADH2 delivers two electrons to complex II • Complex III: Cytochrome bc1 complex - aka CoQ-cytochrome c reductase • Cytochrome C - Water-soluble - Mobile carrier • Complex IV: cytochrome c oxidase - Produces one H2O from 2 H+ plus ½ O2 + 2e- - Complexes I, III & IV pump H+ from matrix to intermembrane space (NOT complex II, cyt. C or CoQ)REDOX REACTIONS • NADH (2e-) reduces complex I • FADH (2e-) reduces complex II • CoQ (mobile carrier) transports 2e- from complex I & II to complex III • Complex III (simplified diagram): Cyt. B & Cyt. C1 are e- transport proteins • Cyt. C1 donates 2e- (1e- at a time) to Cyt. C (mobile-carrier) • Cyt. C transports 4e- to complex IV (2 molecules of Cyt. C deliver 2e- each) • Complex IV (simplified diagram w/o Cu centers): Cyt. A (4e-) to Cyt. A3 (4e-) to oxygen • Oxygen (final e- acceptor) 4e- + 4H+ (from matrix) + O2 --> H2O
