KEGG   PATHWAY: sce00020Help
sce00020                    Pathway                                

Citrate cycle (TCA cycle) - Saccharomyces cerevisiae (budding yeast)
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
sce00020  Citrate cycle (TCA cycle)

Ortholog table
sce_M00003  Gluconeogenesis, oxaloacetate => fructose-6P [PATH:sce00020]
sce_M00009  Citrate cycle (TCA cycle, Krebs cycle) [PATH:sce00020]
sce_M00010  Citrate cycle, first carbon oxidation, oxaloacetate => 2-oxoglutarate [PATH:sce00020]
sce_M00011  Citrate cycle, second carbon oxidation, 2-oxoglutarate => oxaloacetate [PATH:sce00020]
sce_M00307  Pyruvate oxidation, pyruvate => acetyl-CoA [PATH:sce00020]
Other DBs
BSID: 856
GO: 0006099
Saccharomyces cerevisiae (budding yeast) [GN:sce]
YCR005C  CIT2; citrate (Si)-synthase CIT2 [KO:K01647] [EC:]
YNR001C  CIT1; citrate (Si)-synthase CIT1 [KO:K01647] [EC:]
YPR001W  CIT3; citrate (Si)-synthase CIT3 [KO:K01647] [EC:]
YLR304C  ACO1; aconitate hydratase ACO1 [KO:K01681] [EC:]
YNL009W  IDP3; isocitrate dehydrogenase (NADP(+)) IDP3 [KO:K00031] [EC:]
YDL066W  IDP1; isocitrate dehydrogenase (NADP(+)) IDP1 [KO:K00031] [EC:]
YLR174W  IDP2; isocitrate dehydrogenase (NADP(+)) IDP2 [KO:K00031] [EC:]
YOR136W  IDH2; isocitrate dehydrogenase (NAD(+)) IDH2 [KO:K00030] [EC:]
YNL037C  IDH1; isocitrate dehydrogenase (NAD(+)) IDH1 [KO:K00030] [EC:]
YIL125W  KGD1; alpha-ketoglutarate dehydrogenase KGD1 [KO:K00164] [EC:]
YDR148C  KGD2; alpha-ketoglutarate dehydrogenase KGD2 [KO:K00658] [EC:]
YPL017C  IRC15; Irc15p [KO:K00382] [EC:]
YFL018C  LPD1; dihydrolipoyl dehydrogenase [KO:K00382] [EC:]
YOR142W  LSC1; succinate--CoA ligase (GDP-forming) subunit alpha [KO:K01899] [EC:]
YGR244C  LSC2; succinate--CoA ligase (GDP-forming) subunit beta [KO:K01900] [EC:]
YJL045W  succinate dehydrogenase SDH1b [KO:K00234] [EC:]
YKL148C  SDH1; succinate dehydrogenase flavoprotein subunit SDH1 [KO:K00234] [EC:]
YLL041C  SDH2; succinate dehydrogenase iron-sulfur protein subunit SDH2 [KO:K00235] [EC:]
YMR118C  SHH3; protein SHH3 [KO:K00236]
YKL141W  SDH3; succinate dehydrogenase cytochrome b subunit SDH3 [KO:K00236]
YLR164W  SHH4; protein SHH4 [KO:K00237]
YDR178W  SDH4; succinate dehydrogenase membrane anchor subunit SDH4 [KO:K00237]
YPL262W  FUM1; fumarase FUM1 [KO:K01679] [EC:]
YKL085W  MDH1; malate dehydrogenase MDH1 [KO:K00026] [EC:]
YOL126C  MDH2; malate dehydrogenase MDH2 [KO:K00026] [EC:]
YDL078C  MDH3; malate dehydrogenase MDH3 [KO:K00026] [EC:]
YGL062W  PYC1; pyruvate carboxylase 1 [KO:K01958] [EC:]
YBR218C  PYC2; pyruvate carboxylase 2 [KO:K01958] [EC:]
YKR097W  PCK1; phosphoenolpyruvate carboxykinase PCK1 [KO:K01610] [EC:]
YER178W  PDA1; pyruvate dehydrogenase (acetyl-transferring) subunit E1 alpha [KO:K00161] [EC:]
YBR221C  PDB1; pyruvate dehydrogenase (acetyl-transferring) subunit E1 beta [KO:K00162] [EC:]
YNL071W  LAT1; dihydrolipoyllysine-residue 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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