amino acid cofactors

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1、AminoAcidCofactorsSecondaryarticleVictorLDavidson,UniversityofMississippiMedicalCenter,Jackson,Mississippi,USAArticleContents.IntroductionAminoacidcofactorsaretypicallymetalororganicionsthatareessentialforelectrophilic.PyruvoylEnzymescatalysis..DehydroalanylEnzymes.QuinoproteinsIntroduction.OtherCr

2、osslinkedAminoAcidCofactors.AminoAcid-basedFreeRadicalsCertainaminoacidresiduesattheactivesitesofenzymestypicallyplaycriticalrolesincatalysis.Theside-chainsofsomeaminoacidresiduesarechemicallywellsuitedtoPyruvoylEnzymesfunctionaselectrondonorsinnucleophiliccatalysis.Ingeneral,aminoacidsdonotfunctio

3、nwellaselectrophilesPyruvoylenzymescompriseaclassofenzymesthatpossess(i.e.electronacceptors).Instead,metalsandorganicacovalentlyboundpyruvoylprostheticgroup(Figure1).cofactors(e.g.pyridoxalphosphateandflavins)areThiscofactorisderivedfromtheposttranslationaltypicallyrequiredbytheenzymetoserveaselectr

4、onmodificationofaserineresidue,anditdoesnotequilibrateacceptors.Metalsandorganiccofactorsarealsousuallywithexogenouspyruvate(Dowhan,1997).Thisclassofrequiredbyenzymesthatcatalysereactionsthatproceedenzymesincludesbacterialhistidinedecarboxylases,bac-viafree-radicalintermediates.Ithasrecentlybeenob-t

5、erialandeukaryoticS-adenosylmethioninedecarboxy-servedthatcertainenzymeshaveevolvedtocircumventthelases,bacterialandeukaryoticphosphatidylserineneedforexogenouscofactors.Alternatively,endogenousdecarboxylases,bacterialandeukaryotic4’-phosphatecofactorsmaybegeneratedbyposttranslationalmodifica-pantot

6、henoylcysteinedecarboxylases,E.coliaspartatetionofaminoacidresiduesonthepolypeptidechaindecarboxylase,andprolinereductasefromClostridium(Table1).Inmostcasestheseendogenousaminoacid-stricklandii.Asisevidentfromthislist,thisclassofderivedcofactorsfunctionaselectrophilesincatalysisandenzymesplaysanimp

7、ortantroleintheformationofsometimesstabilizefree-radicalintermediates.Inmanybiologicallyimportantaminesfromaminoacidsandcases,thepresenceofaminoacidcofactorswasunrecog-aminoacid-derivedsubstrates.nizeduntil