Which of the following parts of contractile proteins has ATPase activity?

Options

A. G-actin
B. LMM
C. HMM
D. Tropomyosin

Answer

To determine which part of contractile proteins has ATPase activity, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Contractile Proteins**:
- In skeletal muscle, the two main contractile proteins are actin and myosin. Actin forms the thin filaments, while myosin forms the thick filaments.

2. **Understand the Structure of Myosin**:
- Myosin is a complex protein made up of monomers called meromyosin. Meromyosin is further divided into two components: light meromyosin (LMM) and heavy meromyosin (HMM).

3. **Focus on the Globular Head**:
- The structure of myosin includes a globular head, a short arm, and a tail. The globular head is crucial for its function.

4. **ATPase Activity**:
- The globular head of heavy meromyosin is where ATPase activity is located. This means it has the ability to hydrolyze ATP, which is essential for muscle contraction.

5. **Cross-Bridge Formation**:
- For muscle contraction to occur, the myosin heads (with ATPase activity) bind to actin, forming cross-bridges. This interaction is vital for the contraction mechanism.

6. **Conclusion**:
- Based on the above points, the part of the contractile protein that has ATPase activity is the globular head of heavy meromyosin in myosin.

### Final Answer:
The part of contractile proteins that has ATPase activity is the **globular head of heavy meromyosin in myosin**.