胺基酸的代谢生合成biosynthesisofaminoacid

Isoleucineisanessentialaminoacid,onlysynthesizedinplantsandbacteria,andrequiredinthedietbyanimals.Inproteins,thehydrophobicisoleucineside-chaintendstoresidewithotherhydrophobicresiduesintheinteriorofglobularproteinsorintransmembranedomains.Isoleucinebiosynthesisbeginswiththecommonmetabolicintermediatepyruvate,theendpointofglycolysis.Thefirststepinisoleucinebiosynthesisrequiresthiaminepyrophosphatetoformacarbanionintermediate.Anothercomponentcomesfromtheaminoacidthreonine,whichisdeaminatedtoproducealpha-ketobutyrate.Alpha-ketobutyrateandtheTPPintermediatereacttoproducealpha-aceto-alpha-hydroxybutyratethatisisomerized,reducedanddehydratedtocreatealpha-keto-beta-methylvalerate.Inthelaststep,valineaminotransferasetransfersanaminogroupfromglutamatetoproduceisoleucine.Theisoleucinepathwayisalmostthesameasthevalinebiosynthesispathway,usingthesameenzymes,andvaryingprimarilyatthefirststepinthepathway.Asakeyenzymeinthesynthesisofleucine,isoleucineandvaline,acetolactatesynthaseisthetargetofseveralherbicidesandmutationofthisenzymeisresponsibleinsomecasesforthedevelopmentofherbicideresistance.

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