Question

In Michaelis-Menten equation when Km=C:

• A. The rate of process is equal to half of maximum rate
• B. Indicates zero-order process
• C. The rate process occurs at a constant rate
• D. Equation becomes identical to first order elimination of drug

Answer 1

The Correct Option is A

The correct option is (A): The rate of process is equal to half of maximum rate.

Answer 2

The question asks what happens in the Michaelis-Menten equation when the drug concentration C equals the Michaelis constant Km. Let's check each option against the mathematics of the equation.

1. The rate of process is equal to half of maximum rate: The Michaelis-Menten equation is written as \( v = \dfrac{V_{max} \cdot C}{K_m + C} \). Substituting \( C = K_m \) gives \( v = \dfrac{V_{max} \cdot K_m}{K_m + K_m} = \dfrac{V_{max} \cdot K_m}{2K_m} = \dfrac{V_{max}}{2} \). This confirms that when C equals Km, the rate is exactly half of the maximum rate.
2. Indicates zero-order process: A zero-order process happens when C is much greater than Km, so the equation simplifies to v being nearly constant, close to Vmax, and independent of concentration. Setting C equal to Km does not create this condition.
3. The rate process occurs at a constant rate: A constant rate independent of concentration is again the hallmark of zero-order kinetics, which requires C to be much larger than Km, not equal to it.
4. Equation becomes identical to first order elimination of drug: First-order behavior appears when C is much smaller than Km, so the equation simplifies to v being roughly proportional to C. Setting C equal to Km does not produce this simplification either.

Direct substitution of C equal to Km into the Michaelis-Menten equation shows the rate becomes exactly half the maximum rate, which is in fact the condition used to determine Km experimentally.

Therefore, the correct answer is the rate of process is equal to half of maximum rate.