Woah Enzymes again? Reflecting some more :)

In my previous posts on enzymes I did a little a history and I did a little introduction, I do hope that you found it interesting and informative. 🙂

In this blog post I would like to go a little more indept.

Michealis – Menten.

Leonor Michaelis Image and

Maude Menten Image

came up with a simple model that accounts for most of the features of enzyme – catalyzed reactions.

In the model the enzyme will reversibly combine with the substrate and form a enzyme – substrate complex, this will yield a product and regenerate the free enzyme. This is represented by the following equation


In the Michaelis -Menten equation it describes how reaction velocity varies with substrate concentration.


The Km in the equation represents Michaelis constant.

There were alot of Assumptions made during the deriving of the Michaelis- Menten rate equation. And they are…..

1. Relative concentrations of E and S: It says that the [S] is greater that the [E], which means the percentage of total substrate bound by the enzyme at any given time is small

2. Steady- state assumption : This says that the ES complex in unchanged over time, the rate of formation of ES is equal to that of the breakdown of ES. This is similar to transition state, and if you cant remember what the transition state is you can just go and read my previous post on enzymes.

3. Initial Velocity: The rate of the reaction is measured as soon as the enzyme and substrate are mixed. At this point the concentration of the product is small.

Now we move on to some important conclusions about Michaelis – Menten Kinetics.

1. Characteristics of Km

Km – (Michaelis constant) it is characteristic of an enzyme and its substrate. Reflecting the affinity of the enzyme for that substrate. It is numerically equal to the substrate concentration at which the reaction velocity is equal to 1/2 Vmax. It also does not vary with the concentration of enzymes.

When you have a small Km it reflects a high affinity of the enzyme for the substrate.

When you have a large Km it reflects a low affinity of the enzyme for the substrate.

2. Order of reactions.