Michaelis-Menten Kinetics

Michaelis- Menten kinetics is a model that helps in understanding the dynamics of enzyme- catalyzed reactions for quantifying the relationship between the concentration of a substrate and the rate of the reaction. The variables from the equation include V, the reaction rate, [S], the substrate concentration, Vmax, the maximum rate achieved by the system and Km, also known as the Michaelis constant, which represents the substrate concentration at which the reaction rate is half of Vmax.

Enzyme Function Review: In order to fully understand the power of the Michaelis-Menten equation, a review of enzyme function is necessary. The enzyme binds to a substrate molecule (at the active site) to form an enzyme-substrate complex. Within the enzyme-substrate complex, the enzyme facilitates the transformation of the substrate into the product. This step lowers the activation energy needed for the reaction, catalyzing the process. After the substrate is converted into the product, the product is released from the enzyme, freeing the enzyme to bind with another substrate molecule and repeat the process.

Types of Inhibition: An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. There are three types of enzyme inhibition that can be represented using Michaelis-Menten kinetics. It is important to note the effects of each inhibitor on both the Vmax and Km, as each inhibitor affects these two variables differently.

1. Competitive Inhibitors: These bind to the active site of the enzyme, directly competing with the substrate. This type of inhibition can be overcome by increasing the substrate concentration. The Vmax remains unchanged because inhibition can be overcome by simply increasing the substrate concentration. (Vmax/↑Km)

2. Non-Competitive Inhibitors: These bind to a site other than the active site (allosteric site), inducing a conformational change that reduces the enzyme’s catalytic activity. This inhibition cannot be overcome by simply increasing substrate concentration. (↓Vmax/Km)

3. Uncompetitive Inhibitors: These bind only to the enzyme-substrate complex, preventing the release of products. This increases the affinity of the enzyme for the substrate, reducing the Km, and also lowers the rate of reaction because product release is prevented.(↓Vmax/↓Km)

Understanding these effects is crucial for studying enzyme mechanisms in biochemistry.

Tips for memorization: Competitive inhibitors are very competitive, and hence they go straight for the active site. Non-competitive inhibitors are nonchalant, so they bind to either the enzyme-substrate complex, or the enzyme itself, unlike the uncompetitive inhibitors that only bind to the enzyme-substrate complex.

Author: Sanjay Adireddi

Reference Article: https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/michaelis-menten-kinetics

ScienceDirect. Michaelis-Menten Kinetics. Michaelis-Menten Kinetics - an overview | ScienceDirect Topics. Accessed July 31, 2024.