PyruvatedehydrogenasecomplexPyruvate losesCO,and2Hydroxyethyl group is3Acetylgroupis transferred7HETPPisformedtransferred to lipoicacidtoCoA0and oxidized to form1CoASHacetyl dihydrolipoateCH,C-SCoAO4o川0Lipoic acidCHCis reoxidized3HCH-C-COOThiamineNAD+SHPyruvatepyrophosphateSH4[FAD]2ProteinNADH +H*CHSCCCH-OHTPPS-SHydroxyethyl TPPLipoic acid(HETPP)PyruvateDihydrolipoyl transacetylaseDihydrolipoyl dehydrogenasedehvdrogenase(dihydrolipoamide(dihydrolipoamidedehydrogenase)acetyitransferase)Thisstepneedssomecofactorsorcoenzymes:TPP（焦磷酸硫胺素），FAD,CoA,NAD+lipoamide（硫辛酰胺）
Pyruvate dehydrogenase complex This step needs some cofactors or coenzymes: TPP (焦磷酸硫胺素）, FAD, CoA, NAD+, lipoamide（硫辛酰胺）
niacin[naiasin],VB3NicotinamideNH2COORiboseAdenosineCH2HOOHNiacinHOHNHHOHflavin["flaevin]OHOHHOHRiboflavinCH2AdenosineHCNHHCOHHONicotinamideadeninedinucleotide (NAD)Flavinadeninedinucleotide (FAD)(b)(c)ThenicotinamidegroupofnicotinamideadenineOxidation and reduction offlavinadeninedinucleotide (FAD)dinucleotide (NAD)is aderivative of the vitamin niacin(also called nicotinicacid orvitamin Ba; see inset)occursattheriboflavingroup(alsoknownasvitaminB2)and undergoes oxidation and reduction.The relatedcompound nicotinamideadenine dinucleotidephosphate (NADP) containsa phosphoryl group attheadenosineC2'position
niacin ['naɪəsɪn], VB3 flavin ['flævɪn]
PyruvatedehydrogenasereactionsStep 1 Catalyzed by E1 (pyruvate dehydrogenase)Pyruvatedecarboxylated Involves thiamine pyrophosphate (TPP) cofactorthiazoliumringHaCNH2Thiaminepyrophosphate(焦磷酸硫胺素）-CH3Hydroxyethyl-TPPOHCHPyruvate
Pyruvate dehydrogenase reactions Step 1 Catalyzed by E1 (pyruvate dehydrogenase) Pyruvate decarboxylated Involves thiamine pyrophosphate (TPP) cofactor
Pyruvate dehydrogenase reactionsStep 2羟乙基 Hydroxyethyl group transferred to lipoamide prosthetic group in E2LipoicacidLys(dihydrolipoyl transacetylase)CH2CH2 Breaks disulfide bond of lipoamideOIHCH2—CH2CH2—CH TPP regeneratedNH—(CH2)4Lipoamide Hydroxyethyl oxidized to acetylLipoamide(硫辛酰胺）
羟乙基 Pyruvate dehydrogenase reactions Step 2 Hydroxyethyl group transferred to lipoamide prosthetic group in E2 (dihydrolipoyl transacetylase) Breaks disulfide bond of lipoamide TPP regenerated Hydroxyethyl oxidized to acetyl
PyruvatedehydrogenasereactionsStep 3 E2 (dihydrolipoyl transacetylase) transfers acetyl group to CoALipoamidenowfullyreduced Energy released in oxidation of hydroxyethyl to acetyl is conserved inthioester bond of acetyl-CoACoenzymeA These events happen in rapid successionAcetyl-CoACoA—SH[sak'sefn]0HCoA—CHHSHSHS
Pyruvate dehydrogenase reactions Step 3 E2 (dihydrolipoyl transacetylase) transfers acetyl group to CoA Lipoamide now fully reduced Energy released in oxidation of hydroxyethyl to acetyl is conserved in thioester bond of acetyl-CoA These events happen in rapid succession [sək'seʃn]