ATP-ase activity found in `:-`

Options

A. Myosin filament
B. Actin filament
C. Both
D. None

Answer

**Step-by-Step Solution:**

1. **Understanding ATPase Activity**: ATPase activity refers to the ability of certain proteins to hydrolyze ATP (adenosine triphosphate), releasing energy that can be used for various cellular processes.

2. **Identifying the Proteins**: In the context of muscle contraction, two key proteins are involved: myosin and actin. Myosin is a motor protein that interacts with actin filaments to facilitate muscle contraction.

3. **Structure of Myosin**: Myosin is composed of two main parts:
- **Heavy Meromyosin**: This part includes the head, neck, and tail regions. The head region is crucial for ATPase activity.
- **Light Meromyosin**: This part does not have ATPase activity.

4. **Function of Myosin Head**: The myosin head binds to exposed sites on actin filaments. This binding is essential for muscle contraction and is coupled with the hydrolysis of ATP, which provides the energy needed for the conformational changes in myosin.

5. **Conclusion**: Given the above information, the ATPase activity is found in the myosin filament, specifically in the heavy meromyosin portion of the myosin protein.

**Final Answer**: ATPase activity is found in **myosin filament**.

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