Select the TRUE statement about Michealis Constant (Km)
**Core Concept**
The Michaelis constant (Km) is a fundamental parameter in enzyme kinetics that represents the substrate concentration at which the enzyme reaches half of its maximum velocity. It is a measure of the affinity of the enzyme for its substrate, with lower Km values indicating higher affinity.
**Why the Correct Answer is Right**
The Km value is a critical determinant of enzyme kinetics, reflecting the binding energy between the enzyme and its substrate. A low Km value signifies that the enzyme binds its substrate with high affinity, resulting in a higher rate of reaction at lower substrate concentrations. This is in contrast to enzymes with high Km values, which exhibit lower affinity for their substrates and require higher substrate concentrations to achieve half-maximal velocity.
**Why Each Wrong Option is Incorrect**
**Option A:** Km is directly proportional to the enzyme's maximum velocity (Vmax). **Incorrect**, as Km is actually inversely related to Vmax; enzymes with high Km values tend to have lower Vmax values.
**Option B:** Km is a measure of the enzyme's catalytic efficiency. **Incorrect**, as Km specifically reflects the enzyme's affinity for its substrate, not its catalytic efficiency.
**Option C:** Km is influenced by the presence of enzyme inhibitors. **Incorrect**, while enzyme inhibitors can affect Km values, Km is a fundamental property of the enzyme-substrate interaction that is not directly influenced by the presence of inhibitors.
**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the relationship between Km and enzyme affinity is: "Low Km = High Affinity, High Km = Low Affinity."
**Correct Answer: B. Km is a measure of the enzyme's affinity for its substrate.**