enzymes 1: overview and mechanism of actionenzymes are catalysts of chemical reacon and can have...
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ENZYMES1:OVERVIEWANDMECHANISMOFACTIONHLeeYuJsuicoJunsay
DepartmentofChemistry
SchoolofScienceandEngineering
AteneodeManilaUniversity1
WHATAREENZYMES?
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EnzymesaremoleculardevicesthatdeterminethepaBernofchemicaltransformaConsinlivingorganisms.MediatethetransformaConofoneformofenergytoanother
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Enzymesaremostlyproteins,butsomeRNAhavebeentoshowntopossesscatalyCcacCvity.CatalysisoccursintheacCvesite.
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EnzymesarecatalystsofchemicalreacConandcanhavespecifictargetsandproducts.
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EnzymesarecatalystsofchemicalreacConandcanhavespecifictargetsandproducts.
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Enzyme Uncatalyzed rate (kun s-1)
Catalyzed rate (kcat s-1)
Rate enhancement (kcat / kun)
OMP decarboxylase 2.8 x 10-16 39 1.4 x 1017
Triose phosphate isomerase
4.3 x 10-6 4,300 1.0 x 109
Carbonic anhydrase 1.3 x 10-1 1 x 106 7.7 x 106
Atleast1,000,000xfaster!!!
EnzymescatalyzeareacConbystabilizingthetransiConstateofthereacCon.TheydonotaffectequilibriumposiCon
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(a) without catalyst; (b) with iron catalyst; (c) with catalase; (d) with heating
Thereare6majorclassesofenzymes:
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1.Oxidoreductase–transferselectronsusuallyintheformofhydrideions(H:–)orhydrogenatoms(H.)
Thereare6majorclassesofenzymes:
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2.Transferases–transfersfuncConalgroupsfromonemoleculetoanother.
Thereare6majorclassesofenzymes:
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3.Hydrolases–cleavageofbondsbyhydrolysis(addiConofH2O)
Thereare6majorclassesofenzymes:
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4.Lyases–Cleavageofbondsbyothermeans(asidefromhydrolysisoroxidaCon),o^enformingnewdoublebondsoraring.
Thereare6majorclassesofenzymes:
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5.Isomerase–TransferoffuncConalgroupswithinamoleculetoyieldisomericforms.
Thereare6majorclassesofenzymes:
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6.Ligase–FormaConofnewbondsbycondensaConcoupledtoATPcleavage
Enzymesmayalsoneedsomenon‐proteincomponenttowork.Thesemoleculesarecalledcofactors.
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Subdividedinto Metals(Zn2+,Mg2+,Ni2+,Mn2+,K+,Mo,Se) Smallorganicmolecules(coenzymes)
CanbeCghtly(prostheCcgroups)orlooselybound(cosubstrates)
holoenzymecofactorApoenzyme =+
VitaminsaresmallorganicmoleculesessenCalinpropergrowthanddevelopment.Theymaybewater‐solubleorwater‐insoluble.
(SEETABLE6.1)
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Metalionshavediverserolesinenzymecatalysis
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ENZYMEACTIONANDREACTIONMECHANISMS
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Catalysisinenzymesoccurinacavityorcle^calledtheacTvesite.Thesecontainsgroupsfromdifferentpartsoftheprotein.
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TheacCvecontainsgroupswhichstabilizeandbindtothesubstratetoformanenzyme‐substrate(ES)complex.ThesubstrateisheldinplacebyweakIMFs.
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SpecificityofbindingdependsonthepreciselydefinedarrangementofatomsinanacCvesite.Therearetwomodelsthatweknowof:
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TheLockandKeyModel(EmilFischer,1890)
Theenzyme’snaCveformhasacrevicethatisaperfectfitforthetargetsubstrate.
SpecificityofbindingdependsonthepreciselydefinedarrangementofatomsinanacCvesite.Therearetwomodelsthatweknowof:
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TheInducedFitModel(DanielKoshland,1958)
EnzymesassumeashapecomplementarytothatofthetransiConstateonlya"erthesubstrateisbound
SpecificityofbindingdependsonthepreciselydefinedarrangementofatomsinanacCvesite.Therearetwomodelsthatweknowof:
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TheInducedFitModel(DanielKoshland,1958)
EnzymesassumeashapecomplementarytothatofthetransiConstateonlya"erthesubstrateisbound
AnothermodelcalledthetransiTonstatemodelstatesthatthesubstrateconformaConintheEScomplexlookssimilartothatoftheTS,butstabilizedbyweakinteracCons(thusEaislowered!).
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Enzymescanworkinavarietyofways:viaacid‐basereacTons,covalentinteracConsorthruthemetalions.
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CanbefromCOOHorNH3+
AbstractedbyCOO‐orNH2
Enzymescanworkinavarietyofways:viaacid‐basereacCons,covalentinteracTonsorthruthemetalions.
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Mechanismofα‐Chymotrypsin1
1Bugg,T.1997.AnIntroduc4ontoEnzymeandCoenzymeChemistry.
Enzymescanworkinavarietyofways:viaacid‐basereacCons,covalentinteracConsorthruthemetalions.
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ByholdingsubstratesandorienTngthemproperly.
Enzymescanworkinavarietyofways:viaacid‐basereacCons,covalentinteracConsorthruthemetalions.
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BystabilizingnegaTvechargeandpolarizingbonds.
Enzymescanworkinavarietyofways:viaacid‐basereacCons,covalentinteracConsorthruthemetalions.
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ByparTcipaTnginredoxreacTons