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 + Pi 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™