1038 CHAPTER 25 The Organic Mechanisms of the Coenzymes • Metabolism
Figure 25.3
The citric acid cycle (also known as the Krebs cycle or the tricarboxylic acid (TCA) cycle)—the series of
enzyme-catalyzed reactions responsible for the oxidation of pyruvate and acetyl-CoA to and for
the entry of pyruvate and acetyl-CoA into the cycle.
1 pyruvate dehydrogenase 5 -ketogutarate dehydrogenase 8 fumarase
2 citrate synthase 6 succinyl-CoA synthetase 9 malate dehydrogenase
3 aconitase 7 succinate dehydrogenase 10 pyruvate carboxylase
4 isocitrate dehydrogenaseaCO 2pyruvate109citrateH 2 O CoASHmalate231CH 3CCOO−Oacetyl-CoACH 2CH 3 CSCoACCOO−COO−CH 2HCOHCOO−COO−OCH 2HOCCOO−CH 2COO−COO−isocitratesuccinate succinyl-CoAfumarate
45-ketoglutarateCHOHCHCOO−CH 2COO−COO−COCH 2CH 2COO−COO−COCH 2CH 2COO−COO−CH 2CH 2COO−SCoAONAD+ + CoASHNAD+ + CoASHNAD+NADH + H+
+NADH + H+ +NADH + H+NAD+HCO 3 − + ATPADP + Pi678GTP +
CoASHFADFADH 2H 2 OGDP +
HPO 32 −HH
CC
COO−−OOCNADH + H+
+ CO 2CO 2CO 2oxaloacetate