1 Enzyme kinetics -- Michaelis Menten kinetics Two approaches:Rapid equilibrium approachQuasi steady state approachAssumptions:Total enzyme concentration remains constant during the reactionAmount of enzyme is very small compared to amount of substrateThe product concentration is so low that the product inhibition is negligible.
2 wherek1= forward rate constant for formation of ES complexk2= backward rate constant for formation of ES complexk3= rate constant for formation of product P
3 some notations…….. e = concentration of enzyme s = concentration of substratep = concentration of product(es) = concentration of enzyme substrate complext = timev = reaction rate or velocity
4 Michaelis Menten kinetics --Rapid equilibrium approach It is assumed that ES complex is established very rapidly (since this equilibrium step is only the formation of weak interaction between E & S)The product releasing step (k3) is very slow…….which determines the rateThe rate of reverse reaction of the second step is negligible
5 The equilibrium constant The rate of product formation, (mol/ l.s)The total enzyme concentration123
6 Get an expression for (es) in known quantities…… Sub. eqn (1) in (3)
7 Now sub. the value of (es) in eqn 2. Michaelis Menten Equation5
8 Three special cases…….. Case I (s=KM) Therefore…….. is a function of enzyme concentration onlyA low value of means that the enzyme has high affinity for the substrateThree special cases……..Case I (s=KM)Case II (s>>KM)Case III (s<<KM)
9 Case I (s=KM) Eqn. (5) => So when s=KM, the rate of reaction is one half of its maximal value.i.e. at which 50% of enzyme active sites are occupied by substrate
13 Michaelis Menten kinetics --Quasi steady state approach This approach is assumed that the change in the intermediate (transition complex) concentration with respect to time is negligible. (pseudo steady state/quasi steady state)---Briggs-Haldane approachi.e.