catalytic mechanism of enzyme reaction：酶反应的催化机理

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1、CatalyticMechanismofEnzymeReactionRemarkablepropertiesofEnzymesascatalysts1.Catalyticpower2.Specificity3.RegulationAd1.CatalyticPower-enzymesincreasetherateofreactionbyasmuchas1012–fold-notmanyexamplesàtocomparebetweentheratesofanenzyme-catalyzedreactionandthereactionoccurringundersimilarconditions(

2、temperature,pHetc)butintheabsenceofenzymeàasitistoolowtobemeasured-Comparisonbetweenenzymaticandnon-enzymaticcatalystsàalsodifficult.Asenzymaticcatalystsoccur:oMuchhigherratesoLowertemperatureItiswellillustratedbytheprocessofnitrogenfixation(N2àammonia)àcatalyzesbynitrogenasecomplex(300K,pHneutral)I

3、ndustrialsynthesisofammoniafromnitrogenandhydrogenàtemp700-900K,pressure100-900atm,withironcatalystAd2.Specificity-enzymeàhighlyspecificbothin:onatureofsubstrateothereactiontheycatalyze-therangeofspecificityvariesbetweenenzymesolowspecificityàthespecificitybaseonbondspecificityex.Peptidase,phoshatas

4、e,esteraseàutilizeawiderangeofsubstrateswhichcontaintherequiredchemicalbondmostlyfordegradativeenzymesbutnotbiosyntheticenzymes.ointermediatespecificityàgroupspecificityex.Hexokinaseàcatalysethephosphorylationofavarietyofsugarsprovidedtheyarealdohexoseoabsolute/nearabsolutespecificity.àonlycatalysea

5、reactionwithasinglesubstrateatanappreciablerateAd3.Regulation-Thecatalyticactivityàregulatedbysmallionsorothermolecules-Ex.ThebreakdownofglycogeninskeletalmuscleCarbohydratereservedàdegradedtogenerateATPàrequiredformusclecontractionThemusclecontractionistriggeredbyreleaseofCa2+fromthesarcoplasmicret

6、iculumàalsoensurethecontinuationofATPproductionFeedbackinhibitionphenomenaàcommoninmanybiosyntheticpathwayEx.BiosyntheticpathwayleadingtothesynthesisofpyrimidinenucleotideàtheendproductUTPandCTPàblockthefirstenzymeàtheyareabletotolimittheflowofmetabolitesintothepathwayandregulatetheirownbiosynthesis

7、HOWENZYMEWORKING·Acatalystworkssimplybyloweringtheenergybarrierofareaction,ΔGº±·Catalystsprovideanalternativeway·thecatalystincreasesthefractionofmoleculesthathaveenoughenergytoattainthetransitionstat