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1、第七章酶Enzyme第一节酶的概念及特点AnIntroductiontoEnzymesMuchofthehistoryofbiochemistryisthehistoryofenzymeresearch.Biologicalcatalysiswasfirstrecognizedanddescribedinthelate1700s,instudiesonthedigestionofmeatbysecretionsofthestomach,andresearchcontinuedinthe1800swithexaminationsoftheco
2、nversionofstarchtosugarbysalivaandvariousplantextracts.Inthe1850s,LouisPasteurconcludedthatfermentationofsugarintoalcoholbyyeastiscatalyzedby“ferments.”一、酶的概念AnIntroductiontoEnzymesHepostulatedthatthesefermentswereinseparablefromthestructureoflivingyeastcells;thisview,call
3、edvitalism(活力论),prevailedfordecades.Thenin1897EduardBuchnerdiscoveredthatyeastextractscouldfermentsugartoalcohol,provingthatfermentationwaspromotedbymoleculesthatcontinuedtofunctionwhenremovedfromcells.FrederickW.Kühnecalledthesemoleculesenzymes.Asvitalisticnotionsoflifewe
4、redisproved,theisolationofnewenzymesandtheinvestigationoftheirpropertiesadvancedthescienceofbiochemistry.AnIntroductiontoEnzymesTheisolationandcrystallizationofureasebyJamesSumnerin1926providedabreakthroughinearlyenzymestudies.Sumnerfoundthatureasecrystalsconsistedentirely
5、ofprotein,andhepostulatedthatallenzymesareproteins.Intheabsenceofotherexamples,thisidearemainedcontroversialforsometime.Onlyinthe1930swasSumner’sconclusionwidelyaccepted,afterJohnNorthropandMosesKunitzcrystallizedpepsin,trypsin,andotherdigestiveenzymesandfoundthemalsotobep
6、roteins.AnIntroductiontoEnzymesDuringthisperiod,J.B.S.HaldanewroteatreatiseentitledEnzymes.Althoughthemolecularnatureofenzymeswasnotyetfullyappreciated,Haldanemadetheremarkablesuggestionthatweakbondinginteractionsbetweenanenzymeanditssubstratemightbeusedtocatalyzeareaction
7、.Thisinsightliesattheheartofourcurrentunderstandingofenzymaticcatalysis.一、酶的概念WiththeexceptionofasmallgroupofcatalyticRNAmolecules,allenzymesareproteins.Theircatalyticactivitydependsontheintegrityoftheirnativeproteinconformation.Ifanenzymeisdenaturedordissociatedintoitssub
8、units,catalyticactivityisusuallylost.Ifanenzymeisbrokendownintoitscomponentaminoacids,its
