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1、第23章柠檬酸循环主要内容TCA准备阶段TCA循环阶段TCA产能计算TCA的调节TCA双重作用TCA背景知识1、为什么称为柠檬酸循环、三羧酸循环（Tricarboxylicacidcycle,TCA）、Krebs循环？在有氧的情况下，葡萄糖酵解产生的丙酮酸氧化脱羧形成乙酰CoA。乙酰CoA经一系列氧化、脱羧，最终生成C2O和H2O并产生能量的过程，称为柠檬酸循环，亦称为三羧酸循环(tricarboxylicacidcycle),简称TCA循环。由于它是由H.A.Krebs（德国）正式提出的，所以又称Kreb
2、s循环。“Itisconvenienttouseabrieftermforthekindofscheme.Itsessentialfeatureistheperiodicformationofanumberofdi-andtricarboxylicacids.Asthereisnotermwhichwouldserveasacommondenominatorforallthevariousacids,itseemedreasonabletonamethecycleafterone,orsome,ofitsc
3、haracteristicandspecificacids.Itwasfromsuchconsiderationsthattheterm"citricacidcycle"wasproposedin1937.”（HansA.Krebs,Thecitricacidcycle,NobelLecture,December11,1953）Krebs,1901-1981BriefhistoryofTCAThefirstmajorinvestigationintotheintermediarymetabolismofox
4、idationwasthatofThunberg,whoexaminedsystematicallytheoxidizabilityoforganicsubstancesinisolatedanimaltissues.Between1906and1920hetestedtheoxidationofover60organicsubstances,chieflyinmuscletissue.Hediscoveredtherapidoxidationofthesaltsofanumberofacids,sucha
5、slactate(乳酸盐),succinate(琥珀酸盐),fumarate(延胡索酸盐),malate(苹果酸盐),citrate(柠檬酸盐),andglutamate(谷氨酸盐).In1932,Krebswasstudyingtheratesofoxidationofsmallorganicacidsbykidneyandlivertissue.Onlyafewofsubstanceswereactiveintheseexperiments---notablysuccinate,fumarate,ace
6、tate,malate,andcitrate.AnimportantdevelopmentcamefromthelaboratoryofSzent-GyorgyiofSzegedin1935,whoconfirmedonpigeonbreastmuscletherapidoxidationoftheC4-dicarboxylicacids-succinic,fumaric,malic,andoxaloaceticacids-andarrivedatthenewconclusionthatthosedicar
7、boxylicacidswerelinkedbyanenzymaticpathwaythatwasimportantforaerobicmetabolism.AdecisivecontributiontothefieldwasmadeinMarch1937byMartiusandKnoop,whodiscoveredα-ketoglutarate(α-酮戊二酸)asaproductofcitrateoxidation.Becauseitwasalreadyknownthatα-ketoglutarateco
8、uldbeenzymaticallyoxidizedtosuccinate,thepathwayfromcitratetooxaloacetatewasseemedas:In1937,Krebsfoundthatcitratecouldbeformedinmusclesuspensionsifoxaloacetateandeitherpyruvateoracetatewereadded.Now,hegetacyc
