扬州大学：《生物化学 Biochemistry》课程教学课件（讲稿）Biochemistry 1_8 Enzyme（Part 1）

Enzyme (Part 1)

Enzyme (Part 1)

KeyPrinciples[kaetallst]Enzymes are powerful biological catalystsEnzymes exhibit a very high degree of specificityEnzymatic reactions occur in specialized pockets calledactivesites.Two concepts explain the catalytic power of enzymes.Many enzymes are regulated

Key Principles  Enzymes are powerful biological catalysts.  Enzymes exhibit a very high degree of specificity.  Enzymatic reactions occur in specialized pockets called active sites.  Two concepts explain the catalytic power of enzymes.  Many enzymes are regulated. ['kætəlɪst]

EnzymesIn 1897,Eduard Buchner:- demonstrated cell-free yeast extracts could fermentsugar to alcohol- showed fermentation was promoted by moleculesthat continued to function when removed from cells

 Enzymes In 1897, Eduard Buchner: - demonstrated cell-free yeast extracts could ferment sugar to alcohol - showed fermentation was promoted by molecules that continued to function when removed from cells

Mostenzymes areproteinsCatalytic activity depends on the integrity of the nativeproteinconformationMolecular weight =ranges from 12,000 to over 1 millionSome enzymes require additional chemical components- cofactor: 1+inorganic ions,such as Fe2+, Mg2+, Mn2+, and Zn2+- coenzyme = complex organic or metalloorganic moleculethat act as transient carriers of specific functional groups

Most enzymes are proteins  Catalytic activity depends on the integrity of the native protein conformation  Molecular weight = ranges from 12,000 to over 1 million  Some enzymes require additional chemical components: - cofactor : 1+ inorganic ions, such as Fe2+, Mg2+, Mn2+, and Zn2+ - coenzyme = complex organic or metalloorganic molecule that act as transient carriers of specific functional groups

Coenzymes as Transient CarriersofAtomsorFunctionalGroupsTable 6-2 Some Coenzymes That Serve as Transient Carriers ofSpecific Atoms or Functional GroupsExamples of chemicalDietaryprecursor inCoenzymegroupstransferredmammalsCOBiocytinBiotin (vitamin B.)CoenzymeAAcyl groupsPantothenicacid (vitamin[paenta"Aenik]泛酸B5)and othercompounds5'-Deoxyadenosylcobalamin (coenzyme B,2)Vitamin Br2H atoms and alkyl groups[raibaflevin]核黄素Flavin adeninedinucleotideElectronsRiboflavin (vitamin B.)LipoateElectrons and acyl groupsNot required in diet[lr'paot]硫辛酸NicotinamideadeninedinucleotideHydride ion (H-)Nicotinic acid (niacin,[.nika"tinik]烟碱的vitamin B,)[.piri'dpksi:n]吡哆醇Pyridoxal phosphateAminogroupsPyridoxine (vitamin Ba)[“fauleit]叶酸TetrahydrofolateOne-carbongroupsFolate (vitamin B,)Thiamine pyrophosphateAldehydesThiamine (vitamin B,)["Saramin]硫胺素

[pæntə ‘ θenɪk ]泛酸 [ ˌraɪbə‘flevɪn ] 核黄素 [ ˌnɪkə‘tɪnɪk ] 烟碱 的 [ˌpɪrɪˈdɒksiːn ] 吡哆 醇 [‘fəʊleɪt ]叶酸 [‘θaɪəmɪn] 硫胺素 [lɪ‘pəʊt] 硫辛酸

Describing enzymes and their additional chemical componentsProsthetic group =coenzyme or metal ion that is very tightly orcovalentlyboundtotheenzymeproteinHoloenzyme=completecatalytically activeenzymetogetherwithitsbound coenzymeand/ormetal ionsApoenzymeorapoprotein=theproteinpartofaholoenzyme

Describing enzymes and their additional chemical components  Prosthetic group = coenzyme or metal ion that is very tightly or covalently bound to the enzyme protein  Holoenzyme = complete catalytically active enzyme together with its bound coenzyme and/or metal ions  Apoenzyme or apoprotein = the protein part of a holoenzyme

Enzymes areclassified bythereactionstheycatalyzeEnzymes are divided into seven classes, each with subclasses.based on the type of reaction catalyzedEach enzyme has a 4-part enzyme commission number (E.Cnumber)andasystematicnameMost enzymes have trivial names

 Enzymes are classified by the reactions they catalyze  Enzymes are divided into seven classes, each with subclasses, based on the type of reaction catalyzed  Each enzyme has a 4-part enzyme commission number (E.C. number) and a systematic name  Most enzymes have trivial names

International Classification ofEnzymesClass numberClass nameTypepfreaction catalyzed1OxidoreductaseTransferofelectrons(hydrideionsorHatoms)2TransferaseGroup transfer3HydrolasesHydrolysis (transferoffunctional groupstowater)4LyasesCleavage of C-C, C-O, C-N, or other bonds byelimination, leaving double bonds or rings, or additionofgroupstodoublebonds5IsomeraseTransfer of groups within molecules to yield isomericforms6LigasesFormation ofC-C,C-S, C-O,and C-N bonds bycondensationreactions coupledtocleavageofgATP orsimilarcofactor7TranslocasesMovementofmoleculesorionsacrossmembranesortheirseparationwithinmembranes

International Classification of Enzymes Class number Class name Type pf reaction catalyzed 1 Oxidoreductase Transfer of electrons (hydride ions or H atoms) 2 Transferase Group transfer 3 Hydrolases Hydrolysis (transfer of functional groups to water) 4 Lyases Cleavage of C-C, C-O, C-N, or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds 5 Isomerase Transfer of groups within molecules to yield isomeric forms 6 Ligases Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage ofg ATP or similar cofactor 7 Translocases Movement of molecules or ions across membranes or their separation within membranes

Enzyme-Catalyzed Reactions TakePlacewithintheActiveSiteactivesite=providesaspecificenvironmentinwhichagivenreactioncanoccurmorerapidlyKeyactive-siteSubstrateaminoacidresiduessubstrate=themoleculethatisboundtotheactivesite and acted upon bythe enzyme

EnzymesAffectReactionRates,NotEquilibriasimpleenzymaticreactionscanbewrittenasE+S=ES=EP=E+P (6-1)whereE,S,andPrepresentthe enzyme,substrate,and productand ES and EP are transient complexes oftheenzyme