`K_(m)` value is expressed as the substrate concentration at

Options

A. `V_(max)`
B. `(1)/(2) V_(max)`
C. `V_(max)xx2`
D. `V_(max)xx4`

Answer

To solve the question regarding the \( K_m \) value, we need to understand what \( K_m \) represents in enzyme kinetics.

### Step-by-Step Solution:

1. **Understanding \( K_m \)**:
- The \( K_m \) value, known as the Michaelis-Menten constant, is a crucial parameter in enzyme kinetics. It indicates the substrate concentration at which the reaction rate is half of the maximum velocity (\( V_{max} \)) of the enzyme.

2. **Defining \( V_{max} \)**:
- \( V_{max} \) is the maximum rate of the reaction when the enzyme is saturated with substrate. At this point, all active sites of the enzyme molecules are occupied by substrate.

3. **Relationship between \( K_m \) and \( V_{max} \)**:
- The \( K_m \) value is specifically defined as the substrate concentration at which the reaction rate is half of \( V_{max} \). This means that when the substrate concentration equals \( K_m \), the rate of reaction is \( \frac{V_{max}}{2} \).

4. **Choosing the Correct Option**:
- Given the options:
- A) \( V_{max} \)
- B) Half of the \( V_{max} \)
- C) \( V_{max} \times 2 \)
- D) \( V_{max} \times 4 \)
- The correct answer is option B: **Half of the \( V_{max} \)**, since \( K_m \) is defined as the substrate concentration at which the reaction rate is half of the maximum rate.

### Final Answer:
The \( K_m \) value is expressed as the substrate concentration at **half of the \( V_{max} \)**.

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