Which of the protein occurs in the Mitotic spindle mainly ?

Options

A. Actin
B. Tubulin
C. Actomyosin
D. Myoglobin

Answer

### Step-by-Step Solution:

1. **Understanding the Mitotic Spindle**: The mitotic spindle is a structure that forms during cell division (mitosis) and is crucial for the separation of chromosomes. It is composed of microtubules that help in organizing and segregating the chromosomes.

2. **Components of the Mitotic Spindle**: The mitotic spindle is primarily made up of microtubules, which are dynamic structures that can grow and shrink. These microtubules are essential for the proper alignment and separation of chromosomes during cell division.

3. **Identifying the Protein**: The main protein that makes up these microtubules is called tubulin. Tubulin is a globular protein that polymerizes to form microtubules, which are key components of the mitotic spindle.

4. **Eliminating Incorrect Options**: The question provides several options:
- **Actin**: This is a protein that forms microfilaments and is primarily involved in muscle contraction and cell motility, not in the mitotic spindle.
- **Ectomyosin**: This is a complex of actin and myosin, involved in muscle contraction, and not related to the mitotic spindle.
- **Myoglobin**: This is a protein that carries oxygen in muscle cells and is not involved in the mitotic spindle.

5. **Conclusion**: Since tubulin is the only protein listed that is directly associated with the formation of the mitotic spindle, the correct answer is tubulin.

### Final Answer:
The protein that occurs in the mitotic spindle mainly is **tubulin**.

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