Reactions of the Krebs Cycle

substrates	enzyme & coenzymes	products	comments
acetyl-CoA and oxaloacetate	citrate synthase	citrate and HSCoA	irreversible inhibited by high [ATP]/[ADP]
citrate	aconitase Fe²⁺	isocitrate	reversible
isocitrate	isocitrate dehydrogenase NAD+	a-ketoglutarate NADH + H+	irreversible inhibited by high [NADH]/[NAD⁺] and ATP/ADP
a-ketoglutarate	aKG dehydrogenase NAD⁺ FAD thiamine pyrophosphate lipoic acid HSCoA	succinyl-CoA NADH + H⁺ and CO₂	irreversible inhibited by high [NADH]/[NAD⁺] and ATP/ADP
succinyl-CoA GDP + Pi	succinate thiokinase	succinate GTP + H₂O HSCoA	the GTP is produced by a “substrate-level” phosphorylation
succinate	succinate dehydrogenase (Complex II of ETS) FAD	fumarate FADH₂	rate dependent on rate of ETS
fumarate + H₂O	fumarase	L-malate	a lyase reaction, reversible
L-malate	malate dehydrogenase NAD⁺	oxaloacetate NADH + H⁺	we’re back at “Go”
Net reaction for the cycle: Acetyl-CoA + 3 NAD⁺ + FAD + GDP + P_i à 2CO₂ + 3(NADH + H⁺) + FADH₂ + GTP
Animated Krebs Cycle presentation by Donald Nicholson, University of Leeds, UK http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/Metabolomics/Key_Resources/Metabolic_Pathways/TCA_Cycle.html http://www.tcd.ie/Biochemistry/IUBMB-Nicholson/animaps.html > The Citric Acid (TCA) Cycle http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/Metabolomics/Key_Resources.html
Krebs cycle videos : search youtube!
An overview of metabolism by Tom Terry of UConn is at http://web.archive.org/web/20050321231147/www.sp.uconn.edu/~bi107vc/fa02/terry/metabolism.html http://www.sp.uconn.edu/~bi107vc/sp02am/terry/krebs_cycle.gif
The Hub of Metabolism by Donald Nicholson, University of Leeds, UK http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/Metabolomics/Key_Resources/Metabolic_Pathways.html http://www.tcd.ie/Biochemistry/IUBMB-Nicholson/gif/01.html
The Krebs Cycle by Michael W. King at Indiana State U http://web.indstate.edu/thcme/mwking/tca-cycle.html
PowerPoint presentation on The Krebs Cycle by Michael W. King at Indiana State U http://web.archive.org/web/20040630141346/http://web.indstate.edu/thcme/mwking/tcacycle.pdf http://web.indstate.edu/thcme/mwking/tcacycle.pdf
Krebs Cycle and oxidative phosphorylation by John C. Pérez at Texas A&M's Natural Toxins Research Center, Kingsville http://web.archive.org/web/20041212203131/http://ntri.tamuk.edu/cell/mitochondrion/krebpic.html http://ntri.tamuk.edu/cell/mitochondrion/krebpic.html
Chime page on Krebs Cycle intermediates from Dr. Grotzinger at Carnegie Mellon U http://www.bio.cmu.edu/Courses/BiochemMols/TCACycle/TCAMain.htm
Aerobic metabolism by Michael J. Farabee at Estrella Mountain CC http://www.estrellamountain.edu/faculty/farabee/biobk/biobookatp.html http://www.estrellamountain.edu/faculty/farabee/biobk/biobookglyc.html
The reactions of the cycle are shown with an animation by Robert J. Huskey of U Virginia at http://wsrv.clas.virginia.edu/~rjh9u/krebs.html

© Ronald W. Rinehart, 2002-7. If there had been any structures on this page, they undoubtedly would have been drawn with one or more of the following: MDL IsisDraw™ , ACD Labs ChemSketch™, or CS ChemDraw™