Which of the following statements best describes the Michaelis-Menten constant (\(K_m\))?

• A. \(K_m\) is the maximum velocity achieved by the enzyme-catalyzed reaction.
• B. \(K_m\) is the substrate concentration at which the reaction velocity is half of \(V_{max}\).
• C. \(K_m\) is the concentration of enzyme required to reach \(V_{max}\).
• D. \(K_m\) is the rate constant for the formation of the enzyme-substrate complex.

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by understanding the concept of the Michaelis-Menten constant (\(K_m\)). It is a key parameter in enzyme kinetics that provides insight into the enzyme's affinity for its substrate. Specifically, \(K_m\) is defined as the substrate concentration at which the reaction velocity is half of the maximum velocity (\(V_{max}\)).
2. Step 2: Analyze the options provided in the problem. The first option states that \(K_m\) is the maximum velocity achieved by the enzyme-catalyzed reaction. This is incorrect because \(K_m\) is not related to \(V_{max}\) directly; \(V_{max}\) is the maximum reaction rate, while \(K_m\) is a measure of substrate concentration.
3. Step 3: Evaluate the second option, which states that \(K_m\) is the substrate concentration at which the reaction velocity is half of \(V_{max}\). This aligns with the definition of \(K_m\) in enzyme kinetics and is the correct description.
4. Step 4: Consider the third option, which claims that \(K_m\) is the concentration of enzyme required to reach \(V_{max}\). This is incorrect because \(K_m\) is related to substrate concentration, not enzyme concentration.
5. Step 5: Review the fourth option, which suggests that \(K_m\) is the rate constant for the formation of the enzyme-substrate complex. This is also incorrect because \(K_m\) is not a rate constant; it is a substrate concentration value that reflects the enzyme's affinity for its substrate.