[Chemistry Class Notes] Michaelis-Menten Kinetics Pdf for Exam

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

 

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.