The protien whose removal enables myosin to bind actin in smooth muscle is

Options

A. tropomyosin
B. caldesmon
C. myosin light chain kinase
D. calmodulin.

Answer

To answer the question, "The protein whose removal enables myosin to bind actin in smooth muscle is," we can follow these steps:

### Step-by-Step Solution:

1. **Understand Muscle Composition**:
- Muscles are made up of two main types of contractile proteins: actin and myosin. Actin forms the thin filaments, while myosin forms the thick filaments.

2. **Identify Proteins in Smooth Muscle**:
- In smooth muscle, actin filaments are associated with tropomyosin, which runs along the length of the actin filaments.

3. **Role of Tropomyosin**:
- Tropomyosin has a regulatory role. It covers the binding sites on actin, preventing myosin from binding to actin when the muscle is in a relaxed state.

4. **Contraction Mechanism in Smooth Muscle**:
- Unlike striated (skeletal) muscle, where troponin is involved, smooth muscle contraction is regulated differently. The binding of calcium ions does not remove troponin in smooth muscle.

5. **Removal of Tropomyosin**:
- In smooth muscle, the removal of tropomyosin is what exposes the binding sites on actin, allowing myosin to bind and initiate contraction.

6. **Conclusion**:
- Therefore, the protein whose removal enables myosin to bind actin in smooth muscle is **tropomyosin**.

### Final Answer:
The protein whose removal enables myosin to bind actin in smooth muscle is **tropomyosin**.

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