The key difference between Km and Vmax is that Km measures how easily an enzyme can be saturated by the substrate, whereas Vmax is the maximum rate at which an enzyme is catalyzed when the enzyme is saturated by the substrate.
Km can be described as the concertation of the substrate at which half of the maximum velocity is achieved. Vmax, on the other hand, can be described as the reaction rate at the state where the enzyme is fully saturated by the substrate.
CONTENTS
1. Overview and Key Difference
2. What is Km
3. What is Vmax
4. Km vs Vmax in Tabular Form
5. Summary – Km vs Vmax
What is Km?
Km can be described as the concertation of a substrate at which half of the maximum velocity is achieved. In other words, it is the concentration of substrate that permits the enzyme to achieve half Vmax. Therefore, an enzyme having a high Km shows a low affinity for its substrate. It also requires a greater concentration of the substrate to achieve Vmax.
The term Km in enzyme activity is discussed under Michaelis-Menten kinetics. It is a common model of enzyme kinetics. This model was named after German biochemist Leonor Michaelis and the Canadian physician Maud Menten. This model is expressed as an equation.
v = d[P]/dt = Vmax([S]/Km+[S])
In the above equation, Vmax is the maximum rate achieved by the system that occurs at the saturated substrate concentration for a given enzyme concentration. Km is the Michaelis constant. If it is numerically equal to the substrate concentration, then the reaction rate is half of the value of Vmax.
Moreover, biochemical reactions with a single substrate are often assumed to show Michaelis-Menten kinetics without the concern of any underlying assumptions of this model.
What is Vmax?
Vmax can be described as the reaction rate at the state where the enzyme is fully saturated by the substrate. This state indicates that all the binding sites are constantly being reoccupied. In other words, Vmax is the maximum reaction rate or velocity of a reaction that is enzymatically catalyzed upon the saturation of the enzyme with its substrate.
It is important to determine the Km and Vmax for a certain enzymatic activity because knowing these values allows us to predict the metabolic fate of the substrate and the relative amount of substrate that will go through each pathway under different conditions. A lower value of Vmax indicates that the enzyme is operating in sub-optimal conditions.
What is the Difference Between Km and Vmax?
The terms Km and Vmax are important in enzymatic kinetics. The key difference between Km and Vmax is that Km measures how easily the enzyme can be saturated by the substrate, whereas Vmax is the maximum rate at which an enzyme is catalyzed when the enzyme is saturated by the substrate.
The following table summarizes the difference between Km and Vmax.
Summary – Km vs Vmax
Km is the concertation of the substrate at which half of the maximum velocity is achieved. Vmax is the reaction rate at the state where the enzyme is fully saturated by the substrate. The key difference between Km and Vmax is that Km measures how easily the enzyme can be saturated by the substrate, whereas Vmax is the maximum rate at which an enzyme is catalyzed when the enzyme is saturated by the substrate.
Reference:
1. “What Are Enzyme Kinetic Assays? an Overview.” Tip Biosystems, 20 Jan. 2022.
Image Courtesy:
1. “Michaelis Menten curve 2” By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia
2. “Enzyme kinetics curve” By ImranKhan1992 – Own work (CC0) via Commons Wikimedia