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Unformatted text preview: k 1 1 MCDB310 Chapter 6: Enzymes E + S ES E + P k1 k cat k2 The MichaelisMenten Model ] S [ ] S [ M max + = K V V ] ES [ cat = k V MichaelisMenten Plot 2 MCDB310 Chapter 6: Enzymes ] S [ ] S [ M max + = K V V k 1 E + S ES E + P k1 k cat k2 What is K M K M is [S] at which V = V max /2 if k1 >> k cat K M = K D of the enzyme/substrate complex 3 MCDB310 Chapter 6: Enzymes k 1 E + S ES E + P k1 k cat k2 1 1 M k k k K cat + = Definition of K M : What are V max and k cat 4 MCDB310 Chapter 6: Enzymes k 1 E + S ES E + P k1 k cat k2 T max ] E [ ] ES [ = = cat cat k V k V Definition of V max : k cat : Turnover number of the enzyme, i.e. how many substrate molecule each enzyme molecule turns over per second under conditions of saturation The LineweaverBurk Plot y = a + b x 5 MCDB310 Chapter 6: Enzymes ] S [ ] S [ M max + = K V V ] S [ 1 1 1 max M max + = V K V V k cat /K M  Catalytic Efficiency Secondorder reaction with k cat /K M being the second order rate constant! 6 MCDB310 Chapter 6: Enzymes ] S [ ] S [ ] E [ ] S [ ] S [ M T cat M max + = + = K k K V V ] S [ ] E [ ] S [ ] E [ M cat T M cat = K k K k V If [S] << K M : k cat /K M  Catalytic Efficiency cannot be faster than frequency with which E and S collide with each other in solution upper limit for k cat /K M is diffusion (10 810 9 M1 s1 ) enzymes with such k cat /K M values have achieved catalytic perfection reaction is catalyzed almost every time enzyme encounters a substrate molecule 7 MCDB310 Chapter 6: Enzymes ] S [ ] E [ T M cat = K k V Enzyme Kinetics Overview over Parameters K M [M]: [S], at which V = V max /2 K M = K D , when k 2 << k1 V max [M/s]: Maximal velocity of the reaction (when [S] is not rate limiting) k cat [s1 ]: Catalytic constant or turnover number ; how much substrate is converted by the specific enzyme per second k cat /K M [M1 s1 ]: Catalytic (kinetic) efficiency (specificity constant); how fast an enzyme works, once it encounters its substrate 8 MCDB310 Chapter 6: Enzymes optimal k cat /K M can be achieved with various combinations of K M and k cat 9 MCDB310 Chapter 6: Enzymes SOD An Enzyme with Perfect Catalytic Efficiency 10 MCDB310 Chapter 6: Enzymes Reactions Involving Several Substrates a) Random b) Ordered 11 MCDB310 Chapter 6: Enzymes c) Pingpong 1/[S1] (mM...
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This note was uploaded on 04/05/2009 for the course MCDB 310 taught by Professor Walter during the Spring '09 term at University of Michigan.
 Spring '09
 Walter
 Enzymes

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