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Kinetics of laccase-catalysed TEMPO oxidation

Kinetics of laccase-catalysed TEMPO oxidation

Kinetics of laccase-catalysed TEMPO oxidation

JournalofMolecularCatalysisB:Enzymatic37(2005)

Kinetics of laccase-catalysed TEMPO oxidation

79–83

Kineticsoflaccase-catalysedTEMPOoxidation

J.Kulysa,b, ,R.Vidziunaitea,b

a

VilniusGediminasTechnicalUniversity,FacultyofFundamentalSciences,DepartmentofChemistryandBioengineering,

SauletekioAvenue11,10223Vilnius,Lithuania

bInstituteofBiochemistry,DepartmentofEnzymeChemistry,Mokslininku12,08662Vilnius,Lithuania

Received31May2005;receivedinrevisedform23September2005;accepted23September2005

Availableonline26October2005

Abstract

TheoxidationofTEMPO(2,2,6,6-tetramethyl-piperidine-1-oxylradical)hasbeenstudiedinthepresenceofrecombinantlaccases(benzene-diol:oxygenoxidoreductase,EC1.10.3.2)fromPolyporuspinsitus(rPpL),Myceliophthorathermophila(rMtL),Coprinuscinereus(rCcL)andRhizoctoniasolani(rRsL)inbuffersolutionpH4.5–7.3andat25 C.AtpH5.5theoxidationconstantcalculatedfromtheinitialrateofTEMPOoxidationwas1.7×104,1.4×103,7.8×102and5.2×102M 1s 1forrPpL,rRsL,rCcLandrMtL,respectively.ThemaximalactivityofrPpL-catalysedTEMPOoxidationwasatpH5.0.ThepKaobtainedinneutralpHrangewas6.2.ThereactivityoflaccasesisinagoodagreementwithlaccasescoppertypeIredoxpotential.

TEMPOoxidationrateincreased541timesinthepresenceof10-(3-propylsulfonate)phenoxazine(PSPX).ThemodelofsynergisticTEMPOandPSPXoxidationwasproposed.ExperimentallyobtainedrateconstantsforrPpL-catalysedPSPXoxidationwereinagoodagreementwiththosecalculatedfromthesynergisticmodel,thereforecon rmingthefeasibilityofthemodel.TheaccelerationofTEMPOoxidationwithhighreactivelaccasesubstratesopensnewpossibilitiesforTEMPOapplicationasamediator.©2005ElsevierB.V.Allrightsreserved.

Keywords:Laccase;Polyporuspinsitus;Myceliophthorathermophila;Coprinuscinereus;Rhizoctoniasolani;2,2,6,6-Tetramethyl-piperidine-1-oxylradical;TEMPO;10-(3-Propylsulfonate)phenoxazine

1.Introduction

Laccasesareclassi edaspolyphenoloxidasesandperformthereductionofoxygentowaterwhileoxidizingthesubstrate[1].Laccasescatalysetheoxidationoflignin,inorganicandorganicmetalcomplexes,anilines,thiolsandphenols[2–4].Becauseoftheirabilitycatalysetheoxidationofaromaticandothervariouscompounds,laccasesarereceivingincreas-ingattentionasapotentialindustrialenzymesinvariousapplications.

Thelaccasesareabletooxidizecertainphenolswitharedoxpotential(E0)valueshigherthantheirown(from0.5to0.8Vver-susNHE)[2].However,manyinorganicandorganiccompoundswithcomparableE0valuesare“bad”laccasesubstratesduetounfavourablekinetics.Undercertainconditionsthesecom-poundscanbeindirectlyoxidizedbylaccaseviathemediationbysmallredox-activesubstrates.

Correspondingauthor.Tel.:+37052744839;fax:+37052744844.E-mailaddress:jkulys@bchi.lt(J.Kulys).

Theroleofmediatorsinanenzymaticoxidationwiththelaccaseshavebeenextensivelydiscussedpreviously[2,3,5–12].Differenttypesofmediators,particularlyphenothiazines,phe-noxazines,N–OHcompoundsandothershavebeenrecognizedfortheirmediatoryfunctioninlaccasecatalysis.Detailedcom-parativestudiesontheinteractionbetweenmediatorandlac-caseremainstobereported[5–9],althoughvariousphysicalandchemicalcharacterizationshavebeencarriedoutonsev-eralwell-knownlaccasemediators[7,13–16].Thediscoveryofnewef cientlaccasesmediatorsandelucidationofmediationmechanism,inparticular,couldfacilitatethesolutionofdiffer-entbiotechnologicalproblems.

2,2,6,6-Tetramethyl-piperidine-1-oxylradical(TEMPO)isoneofmoreeffectivemediators.ItisastableN-oxylradicalandattractsaconsiderableamountofinterestinitsapplica-tioninorganicsynthesis[5,6,17–21].Morespeci cally,ithasbeendescribedasahighlyselectivecatalystintheoxidationofalcohols[5,6,11,12].The“active”formofTEMPOistheoxoam-moniumion[17,18],formedbyoxidationoftheN-oxylradical,asitisproposedforthereactionofTEMPO-catalysedoxidation

1381-1177/$–seefrontmatter©2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.molcatb.2005.09.010

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