KEGG   PATHWAY: hsa00020Help
hsa00020                    Pathway                                

Citrate cycle (TCA cycle) - Homo sapiens (human)
The citrate cycle (TCA cycle, Krebs cycle) is an important aerobic pathway for the final steps of the oxidation of carbohydrates and fatty acids. The cycle starts with acetyl-CoA, the activated form of acetate, derived from glycolysis and pyruvate oxidation for carbohydrates and from beta oxidation of fatty acids. The two-carbon acetyl group in acetyl-CoA is transferred to the four-carbon compound of oxaloacetate to form the six-carbon compound of citrate. In a series of reactions two carbons in citrate are oxidized to CO2 and the reaction pathway supplies NADH for use in the oxidative phosphorylation and other metabolic processes. The pathway also supplies important precursor metabolites including 2-oxoglutarate. At the end of the cycle the remaining four-carbon part is transformed back to oxaloacetate. According to the genome sequence data, many organisms seem to lack genes for the full cycle [MD:M00009], but contain genes for specific segments [MD:M00010 M00011].
Metabolism; Carbohydrate metabolism
BRITE hierarchy
Pathway map
hsa00020  Citrate cycle (TCA cycle)

Ortholog table
hsa_M00003  Gluconeogenesis, oxaloacetate => fructose-6P [PATH:hsa00020]
hsa_M00009  Citrate cycle (TCA cycle, Krebs cycle) [PATH:hsa00020]
hsa_M00010  Citrate cycle, first carbon oxidation, oxaloacetate => 2-oxoglutarate [PATH:hsa00020]
hsa_M00011  Citrate cycle, second carbon oxidation, 2-oxoglutarate => oxaloacetate [PATH:hsa00020]
hsa_M00307  Pyruvate oxidation, pyruvate => acetyl-CoA [PATH:hsa00020]
H00073  Pyruvate carboxylase deficiency
H00469  Mitochondrial DNA depletion syndrome
H00804  Multiple cutaneous and uterine leiomyomata
H01022  Diseases of the tricarboxylic acid cycle
H01225  D-2-hydroxyglutaric aciduria
H02000  Dihydrolipoamide dehydrogenase deficiency
H02004  Fumarase deficiency
H02005  Mitochondrial complex II deficiency
H02006  Alpha-ketoglutarate dehydrogenase complex deficiency
H02113  Infantile cerebellar-retinal degeneration
D10691  Bempedoic acid (USAN/INN)
D11090  Ivosidenib (USAN/INN)
Other DBs
BSID: 82927
GO: 0006099
Homo sapiens (human) [GN:hsa]
1431  CS; citrate synthase [KO:K01647] [EC:]
47  ACLY; ATP citrate lyase [KO:K01648] [EC:]
50  ACO2; aconitase 2 [KO:K01681] [EC:]
48  ACO1; aconitase 1 [KO:K01681] [EC:]
3417  IDH1; isocitrate dehydrogenase (NADP(+)) 1, cytosolic [KO:K00031] [EC:]
3418  IDH2; isocitrate dehydrogenase (NADP(+)) 2, mitochondrial [KO:K00031] [EC:]
3420  IDH3B; isocitrate dehydrogenase 3 (NAD(+)) beta [KO:K00030] [EC:]
3421  IDH3G; isocitrate dehydrogenase 3 (NAD(+)) gamma [KO:K00030] [EC:]
3419  IDH3A; isocitrate dehydrogenase 3 (NAD(+)) alpha [KO:K00030] [EC:]
55753  OGDHL; oxoglutarate dehydrogenase like [KO:K00164] [EC:]
4967  OGDH; oxoglutarate dehydrogenase [KO:K00164] [EC:]
1743  DLST; dihydrolipoamide S-succinyltransferase [KO:K00658] [EC:]
1738  DLD; dihydrolipoamide dehydrogenase [KO:K00382] [EC:]
8802  SUCLG1; succinate-CoA ligase alpha subunit [KO:K01899] [EC:]
8801  SUCLG2; succinate-CoA ligase GDP-forming beta subunit [KO:K01900] [EC:]
8803  SUCLA2; succinate-CoA ligase ADP-forming beta subunit [KO:K01900] [EC:]
6389  SDHA; succinate dehydrogenase complex flavoprotein subunit A [KO:K00234] [EC:]
6390  SDHB; succinate dehydrogenase complex iron sulfur subunit B [KO:K00235] [EC:]
6391  SDHC; succinate dehydrogenase complex subunit C [KO:K00236]
6392  SDHD; succinate dehydrogenase complex subunit D [KO:K00237]
2271  FH; fumarate hydratase [KO:K01679] [EC:]
4190  MDH1; malate dehydrogenase 1 [KO:K00025] [EC:]
4191  MDH2; malate dehydrogenase 2 [KO:K00026] [EC:]
5091  PC; pyruvate carboxylase [KO:K01958] [EC:]
5105  PCK1; phosphoenolpyruvate carboxykinase 1 [KO:K01596] [EC:]
5106  PCK2; phosphoenolpyruvate carboxykinase 2, mitochondrial [KO:K01596] [EC:]
5161  PDHA2; pyruvate dehydrogenase E1 alpha 2 subunit [KO:K00161] [EC:]
5160  PDHA1; pyruvate dehydrogenase E1 alpha 1 subunit [KO:K00161] [EC:]
5162  PDHB; pyruvate dehydrogenase E1 beta subunit [KO:K00162] [EC:]
1737  DLAT; dihydrolipoamide S-acetyltransferase [KO:K00627] [EC:]
C00022  Pyruvate
C00024  Acetyl-CoA
C00026  2-Oxoglutarate
C00036  Oxaloacetate
C00042  Succinate
C00068  Thiamin diphosphate
C00074  Phosphoenolpyruvate
C00091  Succinyl-CoA
C00122  Fumarate
C00149  (S)-Malate
C00158  Citrate
C00311  Isocitrate
C00417  cis-Aconitate
C05125  2-(alpha-Hydroxyethyl)thiamine diphosphate
C05379  Oxalosuccinate
C05381  3-Carboxy-1-hydroxypropyl-ThPP
C15972  Enzyme N6-(lipoyl)lysine
C15973  Enzyme N6-(dihydrolipoyl)lysine
C16254  [Dihydrolipoyllysine-residue succinyltransferase] S-succinyldihydrolipoyllysine
C16255  [Dihydrolipoyllysine-residue acetyltransferase] S-acetyldihydrolipoyllysine
(map 2)
Nishizuka Y (ed).
[Metabolic Maps] (In Japanese)
Tokyo Kagaku Dojin (1980)
(map 3)
Nishizuka Y, Seyama Y, Ikai A, Ishimura Y, Kawaguchi A (eds).
[Cellular Functions and Metabolic Maps] (In Japanese)
Tokyo Kagaku Dojin (1997)
Michal G.
Biochemical Pathways
Wiley (1999)
KO pathway

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