Chapter29 FFA metabolism.ppt

Chapter29FFAmetabolism,Outline,Fattyacidoxidation-oxidation-oxidation-oxidationFormationandutilizationofketonebodiesFattyacidsynthesisRegulationofFFAmetabolism,BetaOxidationofFattyAcids,Knoopshowedthatfattyacidsmustbedegradedbyremovalof2-CunitsAlbertLehningershowedthatthisoccurredinthemitochondriaF.LynenandE.Reichartshowedthatthe2-Cunitreleasedisacetyl-CoA,notfreeacetateTheprocessbeginswithoxidationofthecarbonthatis"beta"tothecarboxylcarbon,sotheprocessiscalled"beta-oxidation",FranzKnoopsclassicexperimentindicatingthatfattyacidsaremetabolicallyoxidizedattheir-carbonatom,CoAactivatesFAsforoxidation,Acyl-CoAsynthetasecondensesfattyacidswithCoA,withsimultaneoushydrolysisofATPtoAMPandPPiFormationofaCoAesterisexpensiveenergeticallyReactionjustbarelybreaksevenwithATPhydrolysisButsubsequenthydrolysisofPPidrivesthereactionstronglyforwardNotetheacyl-adenylateintermediateinthemechanism!,ConnectingtheFFAtoCoA-SH,CarnitineasaCarrier,CarnitinecarriesfattyacylgroupsacrosstheinnermitochondrialmembraneShortchainfattyacidsarecarrieddirectlyintothemitochondrialmatrixLong-chainfattyacidscannotbedirectlytransportedintothematrixLong-chainFAsareconvertedtoacylcarnitinesandarethentransportedinthecellAcyl-CoAestersareformedinsidetheinnermembraneinthisway,Transportofacyl-carnitineintothematrix,rate-limitingstepforoxidationofFAs,-OxidationofFattyAcids,ARepeatedSequenceof4ReactionsStrategy:createacarbonylgrouponthe-CFirst3reactionsdothat;fourthcleavesthe"-ketoester"Products:anacetyl-CoAandafattyacidtwocarbonsshorter,FADH2,NADHThefirstthreereactionsarecrucialandclassic-wewillseethemagainandagaininotherpathways,oxidation-Fattyacidsaredegradedbyrepeatedcyclesofoxidationattheb-carbonandcleavageoftheC-Cbondtoyieldacetateunits,Oxidationoffattyacids:threesteps,onenew,The-oxidationofsaturatedfattyacids,Acyl-CoADehydrogenase,OxidationoftheC-CbondAfamilyofthreesolublematrixenzymesMechanisminvolvesprotonabstraction,followedbydoublebondformationandhydrideremovalbyFADElectronsarepassedtoanelectrontransferflavoprotein,andthentotheETCEnzymeisinhibitedbyametaboliteofhypoglycin(fromakeefruit),Theacyl-CoAdehydrogenasereaction,Fourthreaction:thiolase,aka-ketothiolaseCysteinethiolateonenzymeattacksthe-carbonylgroupThiolgroupofanewCoAattackstheshortenedchain,forminganew,shorteracyl-CoAThisisthereverseofaClaisencondensation:attackoftheenolateofacetyl-CoAonathioesterEventhoughitformsanewthioester,thereactionisfavorableanddrivesotherthree,Mechanismofactionofketoacyl-CoAthiolase,Summaryof-Oxidation,RepetitionofthecycleyieldsasuccessionofacetateunitsThus,palmiticacidyieldseightacetyl-CoAsComplete-oxidationofonepalmiticacidyields106moleculesofATPLargeenergyyieldistheconsequenceofthehighlyreducedstateofthecarbonandcompactstorage(nohydration)offattyacids,YieldofATPduringtheCompleteOxidationofOneMoleculeofPalmitoyl-CoA,b-oxidationchallenges,monounsaturatedFA,polyunsaturatedFA,odd-carbonFA,(-CcontainingCH3group),Verylongchainfattyacid(VLCFA),suchas26:0or24:0,UnsaturatedFattyAcids,Considermonounsaturatedfattyacids:Oleicacid,palmitoleicacidNormal-oxidationforthreecyclescis-3acyl-CoAcannotbeutilizedbyacyl-CoAdehydrogenaseEnoyl-CoAisomeraseconvertsthistotrans-2acylCoA-oxidationcontinuesfromthispoint,b-oxidationofamonounsaturatedfattyacid,PolyunsaturatedFattyAcids,SlightlymorecomplicatedSameasforoleicacid,butonlyuptoapoint:3cyclesof-oxidationenoyl-CoAisomerase1moreroundof-oxidationtrans-2,cis-4structureisaproblem!2,4-Dienoyl-CoAreductasetotherescue!,Odd-CarbonFattyAcids,-Oxidationyieldspropionyl-CoAOdd-carbonfattyacidsaremetabolizednormally,untilthelastthree-Cfragment-propionyl-CoA-isreachedThreereactionsconvertpropionyl-CoAtosuccinyl-CoATheinvolvementofbiotinandB12,Whatabout3-Cleftovers?,thecoenzymeB12reaction,Branched-ChainFattyAcids,Analternativeto-oxidationisrequiredBranchedchainFAswithbranchesatodd-numbercarbonsarenotgoodsubstratesfor-oxidation-oxidationisanalternativePhytanicacid-oxidasedecarboxylateswithoxidationatthealphaposition-oxidationoccurspastthebranch,The-oxidationpathwayforphytanicacidoxidation,Peroxisomal-Oxidation,Peroxisomes-organellesthatcarryoutflavin-dependentoxidations,regeneratingoxidizedflavinsbyreactionwithO2toproduceH2O2VLGFAshavetotransportedintotheperoxisomewiththehelpofABCD1(ATPbindingcassettesubfamilyDmember1)andthenbeoxidizedthere.ABCD1mutationcancauseadrenoleukodystrophy(ALD)Similartomitochondrial-oxidation,butinitialdoublebondformationisbyacyl-CoAoxidaseElectronsgotoO2ratherthane-transportFewerATPsresult,ComparisonofMitochondrialandPeroxisomalfattyacidoxidation,KetoneBodies,AspecialsourceoffuelandenergyforcertaintissuesSomeoftheacetyl-CoAproducedbyfattyacidoxidationinlivermitochondriaisconvertedtoacetone,acetoacetateand-hydroxybutyrateThesearecalled"ketonebodies"Sourceoffuelforbrain,heartandmuscleMajorenergysourceforbrainduringstarvationTheyaretransportableformsoffattyacids!,KetoneBodies-II,InterestingAspectsofTheirSynthesisOccursonlyinthemitochondrialmatrixFirststepisreversethiolaseSecondreactionmakesHMG-CoAThesereactionsaremitochondrialanaloguesofthe(cytosolic)firsttwostepsofcholesterolsynthesisThirdstep-HMG-CoAlyase-issimilartothereverseofcitratesynthase,Formationofketonebodies,Utilizationofketonebodiesinextra-hepatictissues,KetoneBodiesandDiabetes,"Starvationofcellsinthemidstofplenty"Glucoseisabundantinblood,butuptakebycellsinmuscle,liver,andadiposecellsislowCells,metabolicallystarved,turntogluconeogenesisandfat/proteincatabolismIntypeIdiabetics,OAAislow,duetoexcessgluconeogenesis,soAc-CoAfromfat/proteincatabolismdoesnotgotoTCA,butrathertoketonebodyproductionAcetonecanbedetectedonbreathoftypeIdiabetics,FattyAcidBiosynthesis,TheBiosynthesisandDegradationPathwaysareDifferentAsincasesofglycolysis/gluconeogenesisandglycogensynthesis/breakdown,fattyacidsynthesisanddegradationgobydifferentroutesTherearefourmajordifferencesbetweenfattyacidbreakdownandbiosynthesis,TheDifferences,BetweenfattyacidbiosynthesisandbreakdownIntermediatesinsynthesisarelinkedto-SHgroupsofacylcarrierproteins(ascomparedto-SHgroupsofCoASynthesisincytosol;breakdowninmitochondriaEnzymesofsynthesisareonepolypeptideBiosynthesisusesNADPH/NADP+;breakdownusesNADH/NAD+andFAD/FADH2,Comparisonoffattyacidoxidationandfattyacidbiosynthesis,GeneralFeaturesofFFAbiosynthesis,Cellularlocation-cytosolPrimers-acetyl-CoAActivated2-Cunits-malonyl-CoADecarboxylationofmalonyl-CoAandreducingpowerofNADPHdrivechaingrowthChaingrowsto16-carbonsOtherenzymesadddoublebondsandmoreCs,Challenge:Ac-CoAinCytosol,Whatarethesources?Aminoaciddegradationproducescytosolicacetyl-CoAFAAoxidationproducesmitochondrialacetyl-CoAGlycolysisyieldscytosolicpyruvatewhichisconvertedtoacetyl-CoAinmitochondriaCitrate-malate-pyruvateshuttleprovidescytosolicacetateunitsandreducingequivalentsforfattyacidsynthesis,Thecitrate-malate-pyruvateshuttle,Acetyl-CoACarboxylase,The"ACCenzyme"commitsacetatetoFAsynthesisCarboxylationofacetyl-CoAtoformmalonyl-CoAistheirreversible,committedstepinfattyacidbiosynthesisACCusesbicarbonateandATP(andbiotin)E.colienzymehasthreesubunitsAnimalenzymeisonepolypeptidewithallthreefunctions-biotincarboxylcarrier,biotincarboxylaseandtranscarboxylaseMammalianAcetyl-CoACarboxylaseHasTwoMajorIsoforms.TherearetwomajorisoformsofACC.ACC1occursinadiposetissueandACC2occursintissuesthatoxidizebutdonotsynthesizefattyacids,suchasheartmuscle.,Acetyl-CoAcarboxylase-biotintransferscarboxylgroups,Acetyl-CoAcarboxylasereaction,TheAcylCarrierProtein(ACP),Carrierofintermediatesinfattyacidsynthesisa77residueproteininE.coli-withaphosphopantetheinecontaining-SHIntermsoffunction,itsalargeCoAComparisonofACPandCoA,AcylcarrierproteinandcoenzymeA,FattyAcidSynthesisinAnimals,FattyAcidSynthase-amultienzymecomplexDimerof250kDmultifunctionalpolypeptidestherolesofactivesiteserinesonAT&MTSteps3-6repeattoelongatethechain,MammalianFASynthaseDimer,FirstthreestepsofFAsynthesis,Step45ofFASynthesis,Step7andRepeatsofFASynthesis,Elongation,beyondthe16-Clengthofpalmitate,occursinmitochondria.Endoplasmicreticulumenzymesalsoyieldlongerfattyacids.Fattyacidelongationwithinmitochondriaoccursviab-oxidationrunninginreverse,exceptthatNADPHservesaselectrondonorforthefinalreductionstep.Desaturation:Mammaliancellshavelimitedabilitytointroducedoublebondsinfattyacids.Someunsaturatedfattyacidsaredietaryessentials,e.g.,linoleicacid,18:2cisD9,12.Mammaliancellscannotcreatedoublebondsatcertainlocations(e.g.,D12).,FattyAcidModification,ElongationandDesaturationofFA,RegulationofFFAOxidation,Rate-limitingenzymesiscarnitinepalmitoyltransferaseI(CPTI)Itisinhibitedbymalonyl-CoAwhenfattyacidsynthesisisstimulated.Thisinhibitionkeepsthenewlysynthesizedfattyacidsoutofthemitochondriaandthusawayfromthe-oxidationsystem.Inheartmuscle,anoxidativetissuethatdoesnotcarryoutfattyacidbiosynthesis,containsACC2,whosesolefunctionappearstobethesynthesisofmalonyl-CoAtoregulatefattyacidoxidation.,Rate-limitingenzymesisACC1ACC1formslong,activefilamentouspolymersfrominactiveprotomersPalmitoyl-CoA(product)favorsmonomersCitratefavorstheactivepolymericformPhosphorylationmodulatescitrateactivationandpalmitoyl-CoAinhibitionAMP-dependentproteinkinase(AMPK),whichphosphorylates(inactivates)ACC,RegulationofFFASynthesis,RegulationofACC1,