KEGG   PATHWAY: hsa00020Help
Entry
hsa00020                    Pathway                                

Name
Citrate cycle (TCA cycle) - Homo sapiens (human)
Description
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].
Class
Metabolism; Carbohydrate metabolism
BRITE hierarchy
Pathway map
Citrate cycle (TCA cycle)
hsa00020

All organismsOrtholog table
Module
Gluconeogenesis, oxaloacetate => fructose-6P [PATH:hsa00020]
Citrate cycle (TCA cycle, Krebs cycle) [PATH:hsa00020]
Citrate cycle, first carbon oxidation, oxaloacetate => 2-oxoglutarate [PATH:hsa00020]
Citrate cycle, second carbon oxidation, 2-oxoglutarate => oxaloacetate [PATH:hsa00020]
Pyruvate oxidation, pyruvate => acetyl-CoA [PATH:hsa00020]
Disease
H00073  
Pyruvate carboxylase deficiency
H00469  
Mitochondrial DNA depletion syndrome (MDS)
H00804  
Multiple cutaneous and uterine leiomyomata
H01022  
Diseases of the tricarboxylic acid cycle
H01222  
Cowden-like syndrome
H01225  
D-2-hydroxyglutaric aciduria (D-2-HGA)
Other DBs
BSID: 
GO: 
Organism
Homo sapiens (human) [GN:hsa]
Gene
1431  
CS; citrate synthase [KO:K01647] [EC:2.3.3.1]
47  
ACLY; ATP citrate lyase [KO:K01648] [EC:2.3.3.8]
50  
ACO2; aconitase 2, mitochondrial [KO:K01681] [EC:4.2.1.3]
48  
ACO1; aconitase 1, soluble [KO:K01681] [EC:4.2.1.3]
3417  
IDH1; isocitrate dehydrogenase 1 (NADP+), soluble [KO:K00031] [EC:1.1.1.42]
3418  
IDH2; isocitrate dehydrogenase 2 (NADP+), mitochondrial [KO:K00031] [EC:1.1.1.42]
3420  
IDH3B; isocitrate dehydrogenase 3 (NAD+) beta [KO:K00030] [EC:1.1.1.41]
3421  
IDH3G; isocitrate dehydrogenase 3 (NAD+) gamma [KO:K00030] [EC:1.1.1.41]
3419  
IDH3A; isocitrate dehydrogenase 3 (NAD+) alpha [KO:K00030] [EC:1.1.1.41]
55753  
OGDHL; oxoglutarate dehydrogenase-like [KO:K00164] [EC:1.2.4.2]
4967  
OGDH; oxoglutarate (alpha-ketoglutarate) dehydrogenase (lipoamide) [KO:K00164] [EC:1.2.4.2]
1743  
DLST; dihydrolipoamide S-succinyltransferase (E2 component of 2-oxo-glutarate complex) [KO:K00658] [EC:2.3.1.61]
1738  
DLD; dihydrolipoamide dehydrogenase [KO:K00382] [EC:1.8.1.4]
8802  
SUCLG1; succinate-CoA ligase, alpha subunit [KO:K01899] [EC:6.2.1.5 6.2.1.4]
8801  
SUCLG2; succinate-CoA ligase, GDP-forming, beta subunit [KO:K01900] [EC:6.2.1.5 6.2.1.4]
8803  
SUCLA2; succinate-CoA ligase, ADP-forming, beta subunit [KO:K01900] [EC:6.2.1.5 6.2.1.4]
6389  
SDHA; succinate dehydrogenase complex, subunit A, flavoprotein (Fp) [KO:K00234] [EC:1.3.5.1]
6390  
SDHB; succinate dehydrogenase complex, subunit B, iron sulfur (Ip) [KO:K00235] [EC:1.3.5.1]
6391  
SDHC; succinate dehydrogenase complex, subunit C, integral membrane protein, 15kDa [KO:K00236]
6392  
SDHD; succinate dehydrogenase complex, subunit D, integral membrane protein [KO:K00237]
2271  
FH; fumarate hydratase [KO:K01679] [EC:4.2.1.2]
4190  
MDH1; malate dehydrogenase 1, NAD (soluble) [KO:K00025] [EC:1.1.1.37]
4191  
MDH2; malate dehydrogenase 2, NAD (mitochondrial) [KO:K00026] [EC:1.1.1.37]
5091  
PC; pyruvate carboxylase [KO:K01958] [EC:6.4.1.1]
5105  
PCK1; phosphoenolpyruvate carboxykinase 1 (soluble) [KO:K01596] [EC:4.1.1.32]
5106  
PCK2; phosphoenolpyruvate carboxykinase 2 (mitochondrial) [KO:K01596] [EC:4.1.1.32]
5161  
PDHA2; pyruvate dehydrogenase (lipoamide) alpha 2 [KO:K00161] [EC:1.2.4.1]
5160  
PDHA1; pyruvate dehydrogenase (lipoamide) alpha 1 [KO:K00161] [EC:1.2.4.1]
5162  
PDHB; pyruvate dehydrogenase (lipoamide) beta [KO:K00162] [EC:1.2.4.1]
1737  
DLAT; dihydrolipoamide S-acetyltransferase [KO:K00627] [EC:2.3.1.12]
Compound
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
Reference
(map 2)
  Authors
Nishizuka Y (ed).
  Title
[Metabolic Maps] (In Japanese)
  Journal
Tokyo Kagaku Dojin (1980)
Reference
(map 3)
  Authors
Nishizuka Y, Seyama Y, Ikai A, Ishimura Y, Kawaguchi A (eds).
  Title
[Cellular Functions and Metabolic Maps] (In Japanese)
  Journal
Tokyo Kagaku Dojin (1997)
Reference
  Authors
Michal G.
  Title
Biochemical Pathways
  Journal
Wiley (1999)
KO pathway
 

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