Major protein constituent of muscle fibre is

Options

A. Actin
B. Myosin
C. Tropomyosin
D. Reticulin.

Answer

### Step-by-Step Solution:

1. **Understanding Muscle Fiber Composition**:
- Muscle fibers are primarily composed of proteins that facilitate contraction. The two main types of proteins found in muscle fibers are contractile proteins.

2. **Identifying Contractile Proteins**:
- The two main contractile proteins in muscle fibers are **myosin** and **actin**.
- Myosin is classified as a thick filament, while actin is classified as a thin filament.

3. **Determining the Major Protein**:
- Between myosin and actin, myosin is recognized as the major protein constituent of muscle fibers. This is because it plays a crucial role in muscle contraction and is present in greater amounts compared to actin.

4. **Considering Other Proteins**:
- In addition to myosin and actin, there are other proteins such as **troponin** and **tropomyosin** that assist in muscle contraction, but they are not the major constituents.

5. **Conclusion**:
- Therefore, the major protein constituent of muscle fiber is **myosin**.

### Final Answer:
The major protein constituent of muscle fiber is **myosin**.

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