Question

A connection between IC50 and Michaelis-Menten constant by the Cheng-Prusoff equation

Kᵢ=IC₅₀/1+[S]Kₘ

where Kᵢ
is the binding affinity of the inhibitor,IC₅₀
is the functional strength of the inhibitor, [S] is fixed substrate concentration and Kₘ
is the Michaelis constant in the MM equation:

rate=Vₘₐₓ[S]/Kₘ+[S]

where Vₘₐₓis the maximum rate of reaction.

SupposeIC₅₀ of the drug is x. From my understanding that means- the concentration needed to decrease cells viability by 50%. Since Michaelis-Menten constant means the substrate concentration such that the reaction rate is half of maximum, it seems quite the same. What is wrong in my view? Both seems to cause 50%of effictiveness

Answer 1

The Michaelis-Menten constant (Km) and the IC50 value are not the same. KM represents the affinity of an enzyme for its substrate, while IC50 represents the drug concentration needed to inhibit a biological process by 50%.

Step-by-step explanation:

The Michaelis-Menten equation describes the relationship between substrate concentration ([S]) and the initial reaction rate (v) in an enzymatic reaction. The Michaelis constant (Km) is the substrate concentration at which the reaction rate is half of the maximum rate (Vmax). It is a measure of the enzyme's affinity for the substrate.

The IC50 value, on the other hand, is used in pharmacology to measure the concentration of a drug needed to inhibit a specific biological process by 50%. While both KM and IC50 involve a 50% reduction, they represent different concepts.

KM measures the affinity between an enzyme and a substrate, while IC50 measures the inhibitory effect of a drug on a biological process.

So, in summary, KM and IC50 are not the same. KM represents the affinity of an enzyme for its substrate, while IC50 represents the drug concentration needed to inhibit a biological process by 50%.