Myosin ATP ase gets activated in the pressence of __.

Answer

**Step-by-Step Solution:**

1. **Understanding Myosin ATPase**: Myosin ATPase is an enzyme that plays a crucial role in muscle contraction by hydrolyzing ATP to provide energy for the movement of myosin heads.

2. **Role of Calcium Ions**: For muscle contraction to occur, myosin must interact with actin. This interaction is regulated by calcium ions. When calcium ions are present, they bind to troponin, a protein associated with actin filaments.

3. **Conformational Change**: The binding of calcium to troponin causes a conformational change in the troponin-tropomyosin complex, which uncovers the myosin binding sites on the actin filaments.

4. **Activation of Myosin ATPase**: Once the myosin binding sites on actin are exposed, myosin heads can attach to actin. The presence of calcium ions is essential for this process, as they activate myosin ATPase, allowing it to hydrolyze ATP.

5. **Conclusion**: Therefore, myosin ATPase gets activated in the presence of calcium ions, which are crucial for muscle contraction.

**Final Answer**: Myosin ATPase gets activated in the presence of calcium ions.

---