Conversion of porthrombin to thrombin during clotting requires

Options

A. Vitamin K
B. fibrin
C. thrombokinase
D. heparin

Answer

To solve the question regarding the conversion of prothrombin to thrombin during blood clotting, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Prothrombin and Thrombin**:
- Prothrombin is a plasma protein that is converted into thrombin, an enzyme that plays a crucial role in the coagulation process.

2. **Role of Thrombokinase**:
- Thrombokinase, also known as prothrombinase, is an enzyme that catalyzes the conversion of prothrombin into thrombin. This is a key step in the clotting cascade.

3. **Other Options Analysis**:
- **Vitamin K**: While vitamin K is essential for the synthesis of prothrombin and other clotting factors, it does not directly convert prothrombin to thrombin.
- **Fibrin**: Fibrin is the product formed from fibrinogen by thrombin, but it is not involved in the conversion of prothrombin to thrombin.
- **Heparin**: Heparin is an anticoagulant that prevents blood clotting and does not play a role in the conversion process.

4. **Conclusion**:
- The correct answer to the question is **C) Thrombokinase**, as it is the enzyme responsible for converting prothrombin into thrombin during the clotting process.

### Final Answer:
C) Thrombokinase