Michaelis-Menten Kinetics

Dhristi JEE 2022-24

What is Michaelis Menten Hypothesis?

The Michaelis Menten hypothesis or Michaelis Menten kinetics is a model that is designed to explain generally the velocity of enzyme-catalyzed reactions and their gross mechanism. Among the best-known models in biochemistry to determine catalyst kinetics, the Michaelis Menten hypothesis is used. 

 

The Michaelis Menten kinetics was first proposed in 1913, assuming that enzymes and their substrate are able to form a reversible complex as soon as they react. Substrates are the substances that catalysts react with in order to produce the desired product. A second assumption is that the concentration of the product (p) directly relates to the rate of its formation.

 

Michaelis Menten Equation

Whenever enzyme active sites are filled with substrates, the rate of such a reaction is maximum. In other words, the reaction kinetics increase as the concentration of substrates increases. Kinetic studies of enzymes have been based on this relationship. Thus, the Michaelis Menten hypothesis or the kinetics theory has been reduced to a mathematical formula relating the concentration of the substrate S to the rate of formation of product P or reaction rate v. The formula is stated below that is known as the Michaelis-Menten equation. 

\[{V = \frac {dPP} {dt}}\] = \[{V_{max} = \frac {SS} {K_m + SS}}\]

In this equation, Vmax represents the maximum reaction rate achieved by the system at saturation of the substrate concentration. KM  equals the concentration of the substrate when the value of the rate of reaction is half of Vmax. When the reaction rate and concentration of the substrate of an enzyme-catalyzed reaction are plotted together, the hypothesis becomes clearer.

 

Enzyme-catalyzed Reactions: Mechanism

An enzyme-catalyzed reaction happens when it attracts substrates to its active site and catalyzes them into a desired product. At the end of the reaction process, the product dissociates from the enzyme's active site. A substrate complex is a result of the interaction between the active enzyme and the substrate. 

 

Binary complexes, which involve only one enzyme in the reaction, and ternary complexes, which involve two enzymes and two substrates, are called so. They are connected by electrostatic forces or by hydrophobic forces, not chemical bonds. So, bonding has a physical nature and is noncovalent. 

 

It has been observed that applications of enzymes to biochemical reactions actually increase their rate by a large fraction, approximately 106 times greater than when enzymes are not utilized as catalysts. Additionally, it has been observed that the mechanism of enzyme-catalyzed reactions has the capability of separating very similar substrates and greatly enhancing the rate of reaction of one without having much impact on the other substrate.

 

There is a simple lock and key model popularly known to explain the mechanism behind enzyme-catalyzed reactions. By visualizing the enzyme as three-dimensional and the substrate as three-dimensional, the kinetic model can be clarified. Both the substrates and enzymes are complemented in such a way that their structures can fit tightly with one another and their active catalytic sites are in close proximity to those chemical bonds which are altered during the reaction. As in the case of keys, their active sites are designed to fit perfectly into the keyholes of the locks. Likewise, their active sites are tailored to fit perfectly with the chemical structure of their substrates.

 

Michaelis Menten Kinetics Application

Enzymes 

KM (M)

Kcat (S-1)

Kcat / KM (M-1 S-1)

Chymotrypsin 

1.5 * 10-2

0.14

9.3

Pepsin 

3.0 * 10-4

0.50

1.7 * 103

T-RNA synthetase

9.0* 10-4

7.6

8.4 * 103

Carbonic anhydrase

2.6 * 10-2

4.0 * 105

1.5 * 107

Ribonuclease

7.9 * 10-3

7.9 * 102

1 * 105

 

A catalyst's efficiency is measured by Kcat / KM, a measure of how efficiently it transforms the substrate into a product. So, diffusion enzyme catalysts, such as fumarase, whose upper limit is 108-1010 M-1 S-1, actually diffuse the substrate into the active site of the enzyme catalyst. Apart from biochemical reactions, it has been applied to a wide variety of other areas such as alveolar dust clearance, clearance of blood-alcohol, bacteriophage infection, and photosynthesis-irradiance relationships.

FAQs on Michaelis-Menten Kinetics

1. What Does Michaelis Menten Hypothesis Equation Represent?

Michaelis Menten hypothesis equation represents the reaction rate of single substrate and single enzyme catalyst reaction. This equation is used to mathematically relate the Michaelis Menten constant with initial concentration of the substrate, initial reaction rate and the maximum reaction rate.

2. What Does Michaelis Constant Represent?

Michaelis Constant is also known as substrate concentration and represents the concentration of the substrate when the velocity of the reaction rate is half the maximum reaction rate.

3. Why is Michaelis Constant an Important Factor in Enzyme-Catalyzed Reactions?

This factor  is important to determine the kind of interaction that is  taking place between the substrate and the enzyme, as the range of enzymes are vast and they mostly depend on factors like pH, temperature and ionic strength.

4. How is the Michaelis-Menten equation derived?

Using this equation, the initial rate of reaction is expressed as a measurable quantity, which is the concentration of the substrate at the start of the reaction. Every enzyme-substrate pair will have a different Vmax and Km.

5. What is the Michaelis-Menten constant in chemistry?

Michaelis-Menten constants are defined as concentrations at which enzymes work at half their maximum efficiency. About half of the enzyme's active sites are occupied at this point by substrate molecules.

6. Who proposed the Michaelis Menten equation?

Menten and Leonor Michaelis developed a theory that explains enzyme reversible reactions with their substrates in the following year at a Berlin hospital. The Michaelis-Menten hypothesis describes the mechanism and velocity of enzyme reversible reactions with their substrates.

7. What does the Michaelis Constant represent?

The Michaelis Constant is also referred to as substrate concentration and represents the concentration of the substrate when the velocity of the reaction rate is half that of the maximum reaction rate.

8. What is the Michaelis-Menten equation telling us?

Chemical compounds (the first-order kinetics) are mainly eliminated from the body by the Michaelis-Menten equation, but it is also widely used to describe enzymatic rates at different substrate concentrations.

9. How do Michaelis and Menten base their assumptions?

The Michaelis-Menten rule entails three assumptions: the steady-state approximation, the free-ligand approximation, and the rapid equilibrium approximation.


Michaelis Constant is also known as substrate concentration and represents the concentration of the substrate when the velocity of the reaction rate is half the maximum reaction rate.

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