Identify the INCORRECT statement for a competitive reaction.
A. The 𝑉𝑚𝑎𝑥 is unchanged.
B. The dissociation constant (𝐾𝑑
) is increased.
C. 𝐾𝑚 will increase.
D. The intercept on the x-axis will shift towards the left in the Lineweaver-Burk plot.

What You Should Know About Competitive Inhibition

Introduction

Enzyme inhibition plays a crucial role in regulating biochemical reactions. One common type is competitive inhibition, where an inhibitor competes with the substrate for the enzyme’s active site. But which of the commonly stated characteristics is actually incorrect?

Let’s explore how competitive inhibition works and pinpoint the false statement among the options.

Key Characteristics of Competitive Inhibition

In competitive inhibition:

• The inhibitor resembles the substrate and binds to the active site of the enzyme.
• It can be overcome by increasing the substrate concentration.

Let’s review each of the provided statements:

A. Vmax is unchanged

✅ This is true. In competitive inhibition, the maximum reaction velocity (Vmax) remains the same because a high enough substrate concentration can outcompete the inhibitor.

B. The dissociation constant (Kd) is increased

✅ This is true. Competitive inhibition increases the apparent Kd (a measure of enzyme-substrate affinity), as the inhibitor competes for the same site.

C. Km will increase

✅ Also true. In the presence of a competitive inhibitor, Km (Michaelis constant) increases, reflecting the need for more substrate to reach half of Vmax.

D. The intercept on the x-axis shifts left in the Lineweaver-Burk plot

❌ This is incorrect. In a Lineweaver-Burk plot, competitive inhibition causes the x-intercept (which is -1/Km) to shift right, not left, because Km increases. The slope increases, but Vmax remains unchanged, so the y-intercept stays constant.

✅ Correct answer: D. The intercept on the x-axis will shift towards the left in the Lineweaver-Burk plot is the incorrect statement.

Visualizing with Lineweaver-Burk Plot

In competitive inhibition:

• Lines intersect on the y-axis (Vmax unchanged).
• As Km increases, -1/Km moves closer to zero (shifts right).

Conclusion

Competitive inhibition is well-understood in enzyme kinetics. While Vmax remains the same and Km increases, a common misconception lies in interpreting Lineweaver-Burk plots.

Remember: In competitive inhibition, the x-intercept moves right, not left.

Key Phrase:

Incorrect statement about competitive inhibition