Michaelis menten

Michaelis menten

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  Presentation on Michaelis -Mentenequation 12/14/2018 1
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  PRESENTED BY: Khondaker AfrinaHoque . ID: 1114015 , Reg:900048 Sesssion: 2011-2012. Department of chemistry. Comilla University. 12/14/2018 2
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  • The principalfeatures of many enzyme-catalysed reactions are as follows: 1. For a given initial concentration of substrate, [S]0, the initial rate of product formation is proportional to the total concentration of enzyme, [E]0. 2 For a given [E]0 and low values of [S]0, the rate of product formation is proportional to [S]0. 3 For a given [E]0 and high values of [S]0, the rate of product formation becomes independent of [S]0, reaching a maximum value known as the maximum velocity,vmax. Features of many enzyme-catalysed reactions 12/14/2018 3
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  Michaelis -Menten hypothesis •Invention: Michaelis and Menten , 1913. • Basis: According to this mechanism, an enzyme–substrate complex is formed in the first step and either the substrate is released unchanged or after modification to form products: 12/14/2018 4
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  Michaelis-menten equation productsubstrate Enzymesubstrate complex Free enzyme Rate of the reaction, ν0 = k2[ES]………………………………(1) 12/14/2018 5
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  Calculation of [ES]: Twoways: • Michaelis and Menten assumption, k-1 >> k2. • steady state assumption. Under the conditions: k-1 >> k2 , [S]0 ›› [E]0 ,and KS = k-1/k1 Michaelis -Menten assumption [ES] = [E]0[S] / KS + [S]………(2). Rate of the reaction, ν0 = Dissociation constant [E] = [E]0 - [ES] [S] = [S]0 - [ES] K2[E]O[S]/Ks+[S]…….3 12/14/2018 6
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  [ES] = k1[E]0[S]/ {k-1 + k1 [S] + k2 }…….4 Rate of the reaction, ν0 = k2 k1[E]0[S] / {k-1 + k1 [S] + k2 } d[ES]/dt = k1[E][S] - k-1[ES] - k2[ES]= 0 ………………… 5ν0 = Where, KM = Michaelis constant = (k-1 + k2)/k1) Michaelis-menten equation However, KM ǂ Ks in general unless k-1 >> k2: steady state assumption K2[E]O[S]/Km+[S] 12/14/2018 7
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  Michaelis- Menten equationin term of Vmax This is the velocity at which all the enzyme molecules are in complex form. That is- Vmax =maximum velocity. i.e., [E]0 = [ES], V0=Vm From eqn 1 [E]0 =Vm/k2 Now from eqn (5) ν0 = ……………………6 Fig1:Thevariationof therateof anenzyme-catalysed reactionwithsubstrateConcentration.Theapproachto maximumrate,Vmax,forlarge[S]isexplainedby the Michaelis–Mentenmechanism. 12/14/2018 8
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  Limiting cases 1:At lowsubstrate concentration, KM >> [S] ν0 ≈ ………………………… 7 Thus the rate is of 1st order and depends on the concentration of [S]. ν0 [S] Slope = Fig2: V0 vs. [S] 2:At high substrate concentration, KM << [S] ν0 ≈ νm The rate is zeroth order in [S]. 12/14/2018 9
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  3: Then, ν0 =νm 2 The value of KM can also be obtained from the plot. When KM = [S] Fig 3 Plotof rateversus[substrate] forenzyme catalyzedreaction. but Vm cannot be determined satisfactorily from this plot. ν0 = 12/14/2018 10
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  Lineweaver –burk ordouble reciprocal plot Fig 4:A Lineweaver–Burk plot for the analysis of an enzyme-catalysed reaction that proceeds by a Michaelis–Menten mechanism and the significance of theinterceptsandtheslope. 12/14/2018 11 Taking reciprocal 1/ν0 = Km/ νm[S] + 1/ νm…….8 Hans lineweaver and Dean burk, 1934. A plot of 1/Vo vs. 1/[s] is called a lineweaver-burk or double- receprocal plot , yields a straight line with an intercept of 1/Vmax and a slope of Km/Vmax. The intercept on the x-axis is - 1/Km.
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  Significance of Vmand Km Significance of νm: ν0= here: νm= maximum rate attainable i,e total enzyme conc . Present is equal to enzyme substrate concentration. Significance of Km ν0 = ………………………… (ii) Where, KM = Michaelis constant = (k-1 + k2)/k1) here K2 =Turnover number K2[E]O[S]/Km+[S] ………………………… (i) 12/14/2018 12
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  • Turnover number: Thenumber of substrate molecules converted into products per unit time when the enzyme is fully complexed with substrate as ES. • Three cases arises: i. When k-1 >> k2 Then, Km= Ks. Km becomes the measure of the strength ES complex. ii. Km larger= weak binding iii. Km smaller = stronger binding. Dependence: pH, temperature, substrate etc. Value: KM lies between 10-1 and 10-6 M. 12/14/2018 13
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  Application of michaelis-mentenhypothesis 12/14/2018 14 Enzyme Km Kcat Kcat/Km (catalytic co-efficiency) Chymotrypsin 1.5x10-2 0.14 9.3 Pepsin 3.0x10-4 0.50 1.7x103 Ribonuclease 7.9x10-3 7.9x102 1.0x105 Carbonic anhydrase 2.6x10-2 4.0x105 1.5x107 Fumarase 5.0x10-6 8.0x102 1.6x108 Other applications: Clearence of blood alcohol. Photosynthesis-irradiance relationship. And bacterial phage infection.
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  THANKS TO ALL…….. 12/14/201815