1Enzyme 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.
2wherek1= forward rate constant for formation of ES complexk2= backward rate constant for formation of ES complexk3= rate constant for formation of product P
3some notations…….. e = concentration of enzyme s = concentration of substratep = concentration of product(es) = concentration of enzyme substrate complext = timev = reaction rate or velocity
4Michaelis 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
5The equilibrium constant The rate of product formation, (mol/ l.s)The total enzyme concentration123
6Get an expression for (es) in known quantities…… Sub. eqn (1) in (3)
7Now sub. the value of (es) in eqn 2. Michaelis Menten Equation5
8Three 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)
9Case 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
13Michaelis 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.