Question

In the Michaelis-Menten equation, what does the constant $K_m$ represent?

• A. Maximum reaction velocity
• B. Substrate concentration at half of $V_{max}$
• C. Enzyme concentration
• D. Rate of enzyme degradation

Hint:

$K_m$ = Substrate concentration when reaction rate = $\frac{V_{max}}{2}$

Answer 1

The Correct Option is B

Concept:
The Michaelis–Menten equation describes the relationship between the rate of an enzyme-catalyzed reaction and the concentration of substrate. It is expressed as: \[ v = \frac{V_{max}[S]}{K_m + [S]} \] where:

• $v$ = reaction velocity
• $V_{max}$ = maximum reaction velocity
• $[S]$ = substrate concentration
• $K_m$ = Michaelis constant

Step 1:Understanding the meaning of $K_m$.
The constant $K_m$ represents the substrate concentration at which the reaction rate reaches half of its maximum velocity ($V_{max}/2$).
Step 2:Interpreting enzyme affinity.
The value of $K_m$ also provides information about the affinity of an enzyme for its substrate:

• Low $K_m$ value → High affinity (enzyme binds substrate easily)
• High $K_m$ value → Low affinity (enzyme binds substrate less efficiently)

Step 3:Selecting the correct option.
Since $K_m$ indicates the substrate concentration at which the reaction rate is half of $V_{max}$, option (B) is correct. Conclusion:
Thus, the Michaelis constant $K_m$ represents the substrate concentration required to reach half of the maximum reaction velocity.