4_10_09_TCA Cycle_Enzymatic Reactions

4_10_09_TCA Cycle_Enzymatic Reactions - Berg Tymoczko...

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Biochemistry Sixth Edition Chapter 17: The Citric Acid Cycle Copyright © 2007 by W. H. Freeman and Company   Berg • Tymoczko • Stryer
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α -proteobacterial symbiont archaebacterial host facultative anaerobic “pluripotent” ancestral eukaryote N mitochondrion Hydrogenase PDH PFO ASCT Krebs’ cycle respiratory chain terminal oxidase O terminal oxidases A matrix inner membrane ATP ADP H + mitochondrion ancestral eukaryote gain loss AOX hydrogenase anaerobic respiration PDH PFO ? ASCT Krebs’ cycle (modification to fermentation) terminal oxidase O AOX ATP ADP H + mitochondrion kinetoplastids H + H + Possible scenario of the evolution of the mitochondrion in Kinetoplastida. A facultative anaerobic, 'pluripotent' ancestral eukaryote was formed by endosymbiosis of a facultative anaerobic α -proteobacterium by an archaebacterial host. It has been proposed that different capacities of the original symbiont were lost in different eukaryotic lineages, leading to different types of organelles (aerobic mitochondria, anaerobic mitochondria, hydrogenosomes). In Kinetoplastida, the original hydrogenase, anaerobic terminal oxidases and the capacity to synthesize quinones of low redox potential were lost. Indications for the retainment of the PFO have been reported, but its presence still
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4_10_09_TCA Cycle_Enzymatic Reactions - Berg Tymoczko...

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