The Michaelis constant is a measure of which one of the following?

Options

A. Concentration of the enzyme
B. Catalytic efficiency of the enzyme
C. Thermo-stability of the enzyme
D. Affinity of the enzyme for its substrate

Answer

**Step-by-Step Solution:**

1. **Understanding the Michaelis Constant (Km)**: The Michaelis constant, denoted as Km, is a crucial parameter in enzyme kinetics. It provides insight into how an enzyme interacts with its substrate.

2. **Analyzing the Options**: The question presents several options regarding what the Michaelis constant measures:
- Concentration of enzymes
- Catalytic efficiency of enzymes
- Thermostability of enzymes
- Affinity of enzyme for its substrate

3. **Eliminating Incorrect Options**:
- **Concentration of enzymes**: Km does not measure the concentration of enzymes. This option is incorrect.
- **Catalytic efficiency of enzymes**: While Km is related to enzyme activity, it does not directly measure catalytic efficiency. This option is also incorrect.
- **Thermostability of enzymes**: Km does not provide information about how enzymes behave under heat. This option is incorrect as well.

4. **Identifying the Correct Option**: The only option left is the "affinity of enzyme for its substrate." Km is indeed a measure of how well an enzyme binds to its substrate. A lower Km value indicates higher affinity, while a higher Km value indicates lower affinity.

5. **Conclusion**: Therefore, the Michaelis constant (Km) is a measure of the affinity of an enzyme for its substrate.

**Final Answer**: The Michaelis constant is a measure of the affinity of enzyme for its substrate.

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