3.1general lipid metabolism

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1、SectionI●BiochemistryChylomicrons,VLDL,andIDL(VLDLRemnants)ChylomicronsandVLDLareprimarilytriglycerideparticles,althoughtheyeachhavesmallquantitiesofcholesterolesters.Chylomicronstransportdietarytri-glyceridetoadiposetissueandmuscle,whereasVLDLtranspor

2、ttriglyceridesyn-thesizedinthelivertothesesametissues.BothchylomicronsandVLDLhaveapoC-II,apoE,andapoB(apoB-48onchylomicronsandapoB-100onVLDL).ThmetabolismoftheseparticlesisshowninFigureI-15-6.apoB-48apoB-48TGLTGLADIPOSECECEChylomicronapoC-IIapoEINTESTI

3、NE(lymph)(Epithelium)Chylomicron+Lipoprotein(blood)lipaseapoEapoB-48FattyacidsTGLCholesterolCEGlycerol3-PChylomicronremnantLIVERapoB-100TriglyceridesapoB-100TriglycerideTGLTGLcholcholapoC-IIGlucoseVLDLapoE(blood)Glycerol3-PVLDLLipoprotein(blood)+lipase

4、apoEapoB-100FattyacidsTGLcholIDLFigureI-15-6.ChylomicronandVLDLMetabolismLipoproteinlipaseLipoprotein(LPLase)isrequiredforthemetabolismofbothchylomicronsandVLDL.Thsenzymeisinducedbyinsulinandtransportedtotheluminalsurfaceofcapillaryendothelium,whereiti

5、sindirectcontactwiththeblood.LipoproteinlipasehydrolyzesthefattyacidsfromtriglyceridescarriedbychylomicronsandVLDLandisactivatedbyapoC-II.ChylomicronsChylomicronsareassembledfromdietarytriglycerides(containingpredomi-nantlythelongerchainfattyacids,incl

6、udingtheessentialfattyacids),cholesterolesters,andthefourlipid-solublevitamins.Thecorelipidissurroundedbyphos-pholipidssimilartothosefoundincellmembranes,whichincreasethesolubil-ityofchylomicronsinlymphandblood.ApoB-48isattachedandrequiredforreleasefro

7、mtheepithelialcellsintothelymphatics.224USMLEStep1Biochem.indb22410/18/1610:42AMSectionI●BiochemistryLIPOPROTEINMETABOLISMGeneralConcepts:CholesterolDigestionTriglyceridesandcholesterolaretransportedinthebloodaslipoproteins.Lipoproteinsarenamedaccordin

8、gtotheirdensity,whichincreaseswiththeper-centageofproteinintheparticle.Fromleastdensetomostdense:chylomicrons