Chapter 6b students - k 1 1 MCDB310 Chapter 6: Enzymes E +...

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Unformatted text preview: k 1 1 MCDB310 Chapter 6: Enzymes E + S ES E + P k-1 k cat k-2 The Michaelis-Menten Model ] S [ ] S [ M max + = K V V ] ES [ cat = k V Michaelis-Menten Plot 2 MCDB310 Chapter 6: Enzymes ] S [ ] S [ M max + = K V V k 1 E + S ES E + P k-1 k cat k-2 What is K M K M is [S] at which V = V max /2 if k-1 >> k cat K M = K D of the enzyme/substrate complex 3 MCDB310 Chapter 6: Enzymes k 1 E + S ES E + P k-1 k cat k-2 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 k-1 k cat k-2 T max ] E [ ] ES [ = = cat cat k V k V Definition of V max : k cat : Turn-over number of the enzyme, i.e. how many substrate molecule each enzyme molecule turns over per second under conditions of saturation The Lineweaver-Burk 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 Second-order 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 8-10 9 M-1 s-1 ) 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 << k-1 V max [M/s]: Maximal velocity of the reaction (when [S] is not rate limiting) k cat [s-1 ]: Catalytic constant or turn-over number ; how much substrate is converted by the specific enzyme per second k cat /K M [M-1 s-1 ]: 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) Ping-pong 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.

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Chapter 6b students - k 1 1 MCDB310 Chapter 6: Enzymes E +...

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