In: Chemistry
Michaelis and Menten derived their rate law by assuming a rapid
pre-equilibrium
of E, S, and ES.
a) Derive the rate law in this manner: pre-equilibrium
b) Identify the conditions under which it becomes the same as
that based on the steady·
state approximation.
The rapid equilibrium that Michaelis and Menten considered during their Enzyme Kinetic model,the following equilibrium was considered-
Let's now come to the Steady-State approximation. Here we
consider,the concentration of the intermediate in a multistep
reaction doesn't chnage with time i.e. .Uning
this concept,we now derive the rate law of the above
equilibrium-
Now compare the two equations
i.e equation 5 and eqn 7. The difference is in the expression of
rate constant which is oversimplified in equation 5.So, the
equation 5 can also be alike equation 7 if we did not impose the
condition that " species 'E' 'S' and 'ES'
are considered to be in rapid equilibrium during the entire course
of reaction" i.e the Pre-equilibrium concept
has to be lifted for the intermediate. The only option was then
that the intermediate concentration is constant which is the
Steady-Stare approximation itself.