生化-unit2-中间代谢chapter

BiochemistryChapter9

TricarboxylicAcidCycleThedecarboxylationofpyruvate,andtheoxidationofacetatetakesplaceinthemitochondrialmatrix.ATPsynthesistakesplaceintheinnermembrane.

GlucosePyruvate

Acetal-CoA

TCACycleNAD+NADH+H+CoA-SHCO2CO2+H2OⅠⅢⅡGlycolysisYieldingofacetyl-CoAacetyl-CoAisoxidized

TCATheNobelPrizeinPhysiologyorMedicine1953"forhisdiscoveryofthecitricacidcycle"尿素循环Pyruvateistransportedintomitochondria（线粒体）

thenoxidizedtoacetyl-CoA(releasingCO2)beforeenteringthecitricacidcyclePyruvateisoxidizedtoacetyl-CoA丙酮酸脱氢酶系threeenzymessixcoenzymesPDHcomplexpyruvatedehydrogenase(E1)dihydrolipoyltransacetylase(E2)dihydrolipoyldehydrogenase(E3)CoA-SHNAD+/NADH•H+Lipoate(硫辛酸）FADTPPMg2+RegularproteinsProteinkinasePhosphateproteinphosphatase

Pyruvatedehydrogenasecomplex二氢硫辛酰转乙酰基酶二氢硫辛酸脱氢酶硫胺素焦磷酸Vb1脚气病TheprocessofoxidationfromPyruvatetoacetyl-CoA丙酮酸与TPP结合并脱羧形成羟乙基TPP。2.

羟乙基TPP氧化转变成乙酰基同时转移到E2的辅基硫辛酰胺上。3.在E2上的乙酰基在E2催化下转移到CoASH上形成游离的乙酰CoA.从而形成了一个高能硫酯键。4.还原型的E2将二个SH基H转移到E3的辅酶FAD上形成还原型FADH5.

E3上的还原型的FADH将H交给NAD+形成NADH，E3辅基又形成氧化型的FAD205-660Pyruvatedehydrogenasecomplex二氢硫辛酰转乙酰基酶二氢硫辛酸脱氢酶硫辛酸共价相连ElectronMicrographofpyruvatedehydrogenasecomplexes

受蛋白激酶和磷酸蛋白磷酸酶控制――磷酸化失活E1的磷酸化和去磷酸化是使PDH复合体失活和激活的重要方式.受激素调节受能荷效应物调节（变构调节）激活剂ADP,AMPE1CoASH,NAD+E2,E3抑制剂ATP,GTPE1Acetal-CoANADH•H+E2,E3RegulationofpyruvatedehydrogenasecomplexRegulationofpyruvatedehydrogenasecomplex

砷化物可与丙酮酸脱氢酶复合物中E2辅基硫辛酰胺的巯基发生共价结合，使还原型硫辛酰胺形成失去催化能力的砷化物。拿破仑之死砒霜是如何使拿破仑中毒并死亡的呢？Doyouknow生活中砒霜的形成法国人：继承粉末

虾体内所含砷的化学价是五价，一般情况下，五价砷对人体是没有害处的。理论上讲，高剂量的维生素C（一次性摄入维生素C超过500毫克）和五价砷经过复杂的化学反应，会转变为有毒的三价砷（即我们常说的“砒霜”），当三价砷达到一定剂量时可导致人体中毒。维生素C和虾乙酰CoA柠檬酸顺乌头酸异柠檬酸a-酮戊二酸琥珀酰CoA琥珀酸苹果酸延胡索酸草酰乙酸TricarboxylicAcidCycleEachacetyl-CoAiscompletelyoxidizedtotwoCO2,generatingthreeNADH,oneFADH2,andoneGTP;Themetabolitescontainsix,fiveorfourcarbonsinthecycle.NAD+andFADtakestheelectronsduringacetyl-CoAoxidationThecyclebeginswiththecondensationofacetyle-CoAandoxaloacetatetoformcitrate草酰乙酸柠檬酸柠檬酸合酶Thehydrolysisofthehighenergythioester(硫酯)drivesthereaction.催化TCA的第一步反应，反应先生成柠檬酰CoA，再水解为柠檬酸，是放能反应，不可逆；是TCA的第一个调节酶，活性受ATP、NADH、SuccinylCoA(琥珀酰CoA)及长链脂酰CoA的抑制，对于TCA是一个rate-limitingstep。氟乙酰CoA在酶的作用下可与草酰乙酸生成氟柠檬酸，顺乌头酸酶只识别柠檬酸，对氟柠檬酸没有作用，致使TCA中断，这种合成为致死合成(lethalsynthesis)。在代谢研究的应用上，曾被广泛用于杀虫剂或灭鼠药的生产(现已被明令禁止)。CitricacidsynthaseG0’=8.4kJ/molG0’=-2.1kJ/mol90%4%6%Fluoridecitrate（氟柠檬酸）isthespecialinhbitorofaconitase******Citrateisomerizestoisocitrate(异柠檬酸)

viacis-aconitate(顺乌头酸)Aconitase(乌头酸酶)反应具有严格的空间特异性。Reaction4and5****Isocitrateundergoesoxidativedecarboxylation

(氧化脱羧)toforma-ketoglutarate(a-酮戊二酸)Isocitrateisoxidized(第一次脱氢)anddecarboxylated.(第一次脱羧)既有以NAD+为辅酶的异柠檬酸脱氢酶，也有以NADP+为辅酶的异柠檬酸脱氢酶Positiveeffectors:ADP,AMP,isocitrateNegativeeffectors:

ATP,NADH异柠檬酸脱氢酶Catalyzedby-ketoglutaratedehydrogenasecomplex;almostthesameaspyruvatedehydrogenasecomplex;E3isidentical(相同的),E1andE2areverysimilar.第二次脱氢,第二次脱羧.E1酶不受磷酸共价调节.ReactionrequiresTPPandlipoateetc(6种辅酶).****-ketoglutarateundergoesoxidative

decarboyxlationtoformsuccinyl-CoA(琥珀酰CoA)a-酮戊二酸脱氢酶系**琥珀酰CoA合成酶（也称琥珀酸硫激酶）Cleavageofthethioesterbond(硫酯键)insuccinyl-CoAiscoupledtoGTP(orATP)formationThethirdexampleofsubstrate-levelphosphorylation.琥珀酰CoA琥珀酸琥珀酸是对称分子,没有了手性.Cleavageofthethioesterbond(硫酯键)insuccinyl-CoAiscoupledtoGTP(orATP)formation琥珀酰CoA合成酶琥珀酸延胡索酸Succinateisoxidizedtofumarate(延胡索酸)琥珀酸脱氢酶ThefreeenergychangeofthisreactionisinsufficienttoreduceNAD+.SuccinateDehydrogenaseisdirectlylinkedwiththeelectrontransportchain.三羧酸循环中唯一与内膜结合的酶，是脱氢酶中最重要的酶TCA循环阶段琥珀酸脱氢酶的铁硫聚簇FAD和琥珀酸脱氢酶的共价结合丙二酸琥珀酸（丁二酸）Succinateisoxidizedtofumarate(延胡索酸)1.Theenzymecatalyzesstereospecificdehydrogenation2.Malonate(丙二酸)istheinhibitorofthereaction该酶具有严格的立体专一性，即只生成反式延胡索酸；与琥珀酸结构类似的化合物如丙二酸、戌二酸等是该酶的竞争性抑制剂。延胡索酸苹果酸FumarateishydratedtoL-malate(苹果酸)延胡索酸酶Hydration(水合)该酶具有严格的立体专一性，即只生成L-苹果酸****orOxaloacetate(草酰乙酸)isregeneratedbytheoxidationofL-malate(苹果酸)Thestandardfreeenergyofthisreactionisverypositive.Theoxidationofmalateisdrivenbytheefficientremovaloftheproducts.苹果酸脱氢酶TCA循环阶段苹果酸脱氢酶的结构ThelastthreereactionsoftheoftheTCAcyclearesimilartofattyaciddegradationandsynthesis,andsomeaminoaciddegradations.

oxidation–hydration–oxidation.Amethylenegroup(CH2)isconvertedtoacarbonylgroup(C=O).ThelastthreereactionsoftheoftheTCAcycle1.总反应式:CH3-C-SCoA+3NAD++FAD+GDP+Pi

2CO2+3NADH•H++1FADH2+1GTP+CoA-SH2.Therearetwocarbonatomsintheformofacetyl-SCoAenterseverycycle;andtherearetwodecarboxylationstakeplaceineachcycle;

乙酰辅酶A中的二碳乙酰基进入TCA循环；在循环中发生两次脱羧反应.Notice:the2carbonatomsenteringthecyclearenotthesameasthoseleavingthecycleOSurveyofTCAcycle3.Therearefourdehydrogenationreactionstakeplaceineachcycle;

在循环中发生四次脱氢反应(3NADH,1FADH2)4.Thereisasubstratelevelphosphoralation;

循环中发生一次底物水平磷酸化SurveyofTCAcycle5.Thereactionscatalyzedbyaconitaseandfumaraseisasymmetryreactions;顺乌头酸酶和延胡索酸酶等催化非对称反应6.Alloftheintermediarymetabolismsarenotsynthesisandpositionnet.所有中间代谢产物在代谢中没有净合成或净降解.SurveyofTCAcycleAcetylinacetyl-S-CoAwasoxydized:

化学氧化释放的自由能：874.9kJ/mol

生物氧化释放的自由能：520.9kJ/mol

用于ATP合成的自由能：354kJ/molTheenergeticoftheaerobicpositionofglucose2.HydrationsinTCA-cycle:ThethirdH2OenteredinTCAcycle:Citryl-CoA+H2Osuccinyl-CoA+H2OFumarate+H2OCitrate+CoA-SHSuccidate+CoA-SHMatalteH2OH2OTheenergeticoftheaerobicpositionofglucoseH2O3.Dehydrogenationsinoxydationofglucose:

InEMP:C6H12O62×pyruvate+4HInTCAcycle:2×acetyl-CoA+2×3H2O16H+4CO2

2×CoA-SHSo: C6H12O6+6H2O24H+6CO2

6O2

12H2O

C6H12O6+6O26H2O+6CO2Informationofacetyl-CoA:

2×pyruvate2×CoA-SH2×acetyl-CoA+4H+2CO2Theenergeticoftheaerobicpositionofglucose4.CaculationofenergyInEMP:ATP4-2NumbersofATP2NADH•H+2×2.5Informationofacetyl-CoA:2NADH•H+2×2.5InTCAcycle:3NADH•H+×23×2.5×2FADH2×21×1.5×2GTP×2

1×1×2Summery:32(→FADH2)(2×1.5)(30)TheenergeticoftheaerobicpositionofglucoseThereactionofTCAcycle

1.AllorganicchemicalscanbecompletelyoxidizedtoCO2andH2Oviaacycledpathway;所有的有机化合物都可以通过TCA环彻底降解为CO2和H2O;2.Plentyenergycanbeprovidedpanythecycledpathway;伴随着这一循环途径，大量的自由能被转换;SignificanceofTCA3.Theintermediatesinthecycleareimportantsourcesforbiosyntheticprecursors;TCA环中的中间代谢产物是重要的生物合成的前体4.Thecycleisanamphibolicpathway,andisametabolichingeofallbiochemicalsTCA环是一个分解合成无定向途径，是所有生物化合物的代谢枢纽。分解产能,合成前体.SignificanceofTCAInadditiontogeneratingreducingpotential,theTCAcyclealsoprovidesmoleculesforbiosyntheticpathways.Also,theTCAcycleisanentrypointfordegradativepathwayssuchasaminoacidcatabolism.Thus,theTCAcycleishighlyregulated.TCACycleRegulation(TCA循环的调节)RegulationofthePDHComplexHighconcentrationsofthereactionproductsofthePDHcomplexinhibitactivity:NADHAcetylCoAThismakessensebecauseitindicatesthecellisrichinenergy.RegulationofthePDHComplexThePDHcomplexiscovalentlymodifiedbyphosphorylation.Phosphorylation