Michaelis Menten

(there is another paragraph about the same topic, an extra explanation from literature in 5.7)
Every reaction occurs with a certain reaction rate V and with its own reaction constant k
k1                   k3

k2                
Starting with three presupposition supposing ideal / optimal conditions, you may state that the rate, at its maximum, is Vmax


The three presuppositions are:
  1. a steady stat wherein the concentration of the intermediate ES does not change; the production of the ES complex takes place with the same rate as its disappearance;
  2. Every present enzyme participates;
  3. The system is in an optimal environment (saturated with S, the best pH, the best temperature);
In this way the reaction rate V has ist maximal value Vmax


about the rate of producint the intermediate ES:



about teh rate of the disappearance (to the right and to the left) of that intermediate ES:





KM is the constant of Michaelis

KM shows the affinity of the enzyme for the substrate; a low KM means a lot of ES, or, a lot of substrate S,
and that means: a low KM and a bigger rate.

The relation between the reaction rate and the KM can be seen in the Michaelis Menten equation:



The values of KM    can vary between 0 and thousands.

For a certain standard amount of hexokinase or glycokinase, we measure the production rate (V) of glucose phosphate (The product G6P) as a function of the glucose concentration [S].
The results show that Vmax of the two enzyms are equal (100 nmol G6P are produced per minute), but that the Km-values differ considerably:
Km of hexokinase  = 0.1 mM, Km of glucokinase = 10 nM (factor 100)."

Have again a good look at the following equilibrium with the intermediate SE:
k1                k3


k2                

The constant of Michaelis shows the affinity of the enzyme to the substrate.


The equation of Michaelis-Menten shows the relation between KM and the reaction rate.

We know various types of enzyme inhibitors:
  1. product inhibitors
  2. drugs inhibitors
  3. allosteric inhibitors