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L16-18-Enzyme_Kinetics - Enzyme Kinetics Michealis Menten...

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51 Enzyme Kinetics Michealis Menten Approach to Enzyme Kinetics developed by Leonor Michaelis and Maud Menten in 1913 after confirming results first obtained in 1903 by Henri Henri first observed that the enzyme rate plotted as a function of concentration increased in a non-linear manner until it reached a maximal rate and then leveled off Consider the reaction of a substrate (S) being converted to a product (P) S à P A simplified mechanism can be written as E + S k 1 ES k 2 E + P The rate of formation of product ( v ) is dependent on the amount of enzyme-substrate complex present since that's the only species that goes through catalysis v = d P [ ] dt = k 2 ES [ ] Once an enzyme-substrate complex is formed, it can be broken down in two ways: going to product or going to reactants An important assumption of Michaelis-Menten kinetics is that the concentration of the enzyme substrate complex is nearly constant or at a steady state. d ES [ ] dt = 0 first proposed by Briggs and Haldane more general than the equilibrium assumption proposed by Michaelis and Menten
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52 if [ES] doesn’t change, the rate of formation is equal to the rate of breakdown Rate of formation = Δ ES [ ] Δ t = k 1 E [ ] S [ ] Rate of breakdown = Δ ES [ ] Δ t = k 1 ES [ ] + k 2 ES [ ] k 1 E [ ] S [ ] = k 1 ES [ ] + k 2 ES [ ] Since the reaction is dependent on the concentration of ES we need to find this value, but we have two enzyme terms. ES is unknown, but we can know how much total enzyme we added at the beginning of the experiment. E total = E + ES and [E] = [E] total – [ES] The concentration of S is large relative to the concentration of E and doesn't change much so we assume that the concentration of S is equal to total concentration of S.
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