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1、Howthedivisionof"spoils"cameaboutIdonotrecall-itmayhavebeenbydrawinglots.Atanyrate,DavidShemin"drew"aminoacidmetabolism,whichledtohisclassicalworkonhemebiosynthesis.DavidRittenburBwastocontinuehisinterestinproteinsynthesisandturnover,andlipidsweretobemyterritory.-Kon
2、radBloch,onhowhiscareerturnedtoproblemsoflipidmetabolismafterthedeathofhismentor,RudolfSchoenheimer;articleinAnnualReviewofBiochemistrv.l9B7LipidBiosynthesis21.1BiosynthesisofFattyAcidsandEicosanoids80521.1BiosynthesisofFattyAcids21.2BiosynthesisofTriacylglycerols820
3、andEicosanoids21.3BiosynthesisofMembranePhospholipids824Afterthediscoverythatfattyacidoxidationtakesplacebytheoxidativeremovalofsuccessivetwo-car-21.4Biosynthesisof(holesterol,Steroids,bon(acetyl-CoA)units(seeFig.17-8),biochemistsandlsoprenoids831thoughtthebiosynthes
4、isoffattyacidsmightproceedbyasimplereversalofthesameenzymaticsteps.How-ever,astheyweretofindout,fattyacidbiosynthesisipidsplayavarietyofcellularroles,someonlyIandbreakdownoccurbydifferentpathways,arecat-recentlyrecognized.TheyaretheprincipalformofIalyzedbydifferentse
5、tsofenzymes,andtakeplaceinbstoredenergyinmostorganismsandmajordifferentpartsofthecell.Moreover,biosynthesisre-constituentsofcellularmembranes.Specializedlipidsquirestheparticipationofathree-carbonintermedi-serveaspigments(retinal,carotene),cofactors(vitaminate,malony
6、l-CoA,thatisnotinvolvedinfattyacidK),detergents(bilesalts),transporters(dolichols),breakdown.hormones(vitaminDderivatives,sexhormones),extra-Or..cellularandintracellularmessengers(eicosanoids,,Ophosphatidylinositolderivatives),andanchorsformem--Obraneproteins(covalen
7、tlyattachedfattyacids,prenyl"c-cH'z-cS-CoAgroups,andphosphatidylinositol).Theabilitytosynthe-Malonyl-CoAsizeavarietyoflipidsisessentialtoallorganisms.ThisWefocusflrstonthepathwayoffattyacidsynthesis,chapterdescribesthebiosyntheticpathwaysforsomeofthenturnourattentio
8、ntoregulationofthepathwayandthemostconunoncellularlipids,illustratingthestrate-tothebiosynthesisoflonger-chainfattyacids,unsatu-gie