Globular protein which masks active sites on F-actin is :-

Options

A. Tropomyosin
B. Troponin
C. Myosin
D. Myomesin

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the name of the globular protein that masks the active sites on F-actin.

2. **Identifying F-actin**: F-actin, or filamentous actin, is a polymerized form of globular actin (G-actin) and is a crucial component of the cytoskeleton in muscle cells.

3. **Role of Proteins in Muscle Contraction**: In muscle fibers, the interaction between actin and myosin is essential for muscle contraction. However, during the relaxed state of the muscle, certain proteins prevent this interaction.

4. **Identifying the Key Proteins**: The two key proteins involved in regulating the interaction between actin and myosin are troponin and tropomyosin. Tropomyosin is a long, fibrous protein that wraps around the actin filament and blocks the binding sites for myosin.

5. **Function of Troponin**: Troponin is a globular protein that is associated with tropomyosin. It binds to calcium ions when the muscle cell is stimulated, causing a conformational change that moves tropomyosin away from the binding sites on actin.

6. **Conclusion**: The globular protein that masks the active sites on F-actin is **troponin**.

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