Question

Following are the data of substrate concentration and the corresponding velocity of an enzyme:
Substrate concentration in mM: 10, 30, 60, 100, 120, 160, 200, 250, 300
Enzyme velocity in IU: 20, 40, 60, 80, 100, 140, 160, 200, 220
On the basis of the above data, Km value of the enzyme is:

• A. 60 mM
• B. 100 mM
• C. 120 mM
• D. 200 mM

Hint:

Km = [S] at Vmax/2.
Lower Km = higher affinity.
Vmax is the maximum velocity.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Km is the substrate concentration at which velocity is half of Vmax.
It is a measure of enzyme affinity for substrate.

Step 2: Key Formula or Approach:
Vmax is the maximum velocity.
Km is the substrate concentration at Vmax/2.

Step 3: Detailed Explanation:
From the data:
[S] = 10, V = 20.
[S] = 30, V = 40.
[S] = 60, V = 60.
[S] = 100, V = 80.
[S] = 120, V = 100.
[S] = 160, V = 140.
[S] = 200, V = 160.
[S] = 250, V = 200.
[S] = 300, V = 220.
Vmax is approximately 220 IU.
Vmax/2 = 110 IU.
From the data, V = 100 IU at [S] = 120 mM.
V = 140 IU at [S] = 160 mM.
V = 110 IU would be between 120 and 160 mM.
Thus, Km is approximately 120 mM.

Step 4: Final Answer:
The Km value of the enzyme is 120 mM.
Hence, the correct option is (C).