Enzymatic_reaction_kinetics.ppt

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1、Section5EnzymaticReactionKinetics5.1TheeffectsofsubstrateconcentrationonreactionrateSubstratesaturationcurveforanenzyme-catalyzedReaction.Theamountofenzymeisconstant,andtheVelocityofthereactionisdeterminedatvariousSubstrateconcentration.*Atlowconcentration,thereactionrateisincr

2、easedastheincreaseofsubstrateconcentration.dp/dt=k[S]*Atrelativehighconcentration,thereactionrateisincreasedastheincreaseofsubstrateconcentration,buttheincreaserateisnotindirectproportion*Athighconcentration,thereactionrateisnotincreasedastheincreaseofsubstrateconcentration.dp/d

3、t=k[Et]WhereEtisthetotalconcentrationofenzymeTherelationshipofreactionrateandsubstrateconcentrationcanbeexplainedbyintermediatetheory.E+S=ES→E+PThemaximalratemeansalltheenzymearesaturatedbysubstrates.k1k3E+S=ES→E+Pk2Theenzyme(E),combineswithitssubstrate(S)toformanenzyme-substrat

4、ecomplex(ES).The(ES)complexcandissociateagaintoformE+S,orcanproceedchemicallytoformEandtheproductP.Themichaelis-Mentenequation:1913Michaelis-mentenconstantKm(米氏常数)Vmax/2=Vmax.[S]/Km+[S]Km=[S]KmisequivalenttothesubstrateconcentrationatwhichthevelocityisequaltohalfofVmax.米氏常数是酶促反应

5、速度为最大反应速度一半时的底物浓度。SignificancesofKmAmeasureoftheaffinity(亲和力)ofanenzymeforitssubstrateKmisameasureofthestabilityoftheEScomplex,beingequaltothesumoftheratesofbreakdownofESoveritsrateofformation.Formanyenzymesk2ismuchgreatthank3.ThevalueofKmdependsontherelativevaluesofk1andk2forfo

6、rmationanddissociation,respectively.Km=(k2+k3)/k1AhighKmindicatesweaksubstratebinding(k2predominantoverk1),alowKmindicatesstrongsubstratebinding(k1predominantoverk2)问题：如果已知一种酶有几种底物，如何确定最佳底物？Kmisthespecifictoagivenenzyme.Itisthefeaturingconstantofenzyme.Atgivenconditionandsubstra

7、te,anenzymehasitsspecificKmtothesubstrate.MeasurementofKmBecauseVmaxisachievedatinfinitesubstrateconcentration,itisimpossibletoestimateVmax(andhenceKm)fromahyperbolicplot双曲线.VmaxandKmcanbedeterminedexperimentallybymeasuringvatdifferentsubstrateconcentrations.（a）估计V和Km，（b）在[S]=2.

8、5×10-5molL-1和[S]=5.0×10-5molL-1时，v会是多大？Lineweav