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 the clotting process, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Prothrombin and Thrombin**:
- Prothrombin is an inactive precursor of thrombin, which is an active enzyme involved in blood coagulation.

2. **Role of Thrombokinase**:
- The conversion of prothrombin to thrombin is facilitated by an enzyme complex known as thrombokinase (also referred to as prothrombinase). This enzyme complex catalyzes the reaction that activates prothrombin.

3. **Process of Clotting**:
- During the clotting process, when there is an injury, various factors in the blood are activated. Thrombokinase is one of these factors and plays a crucial role in the coagulation cascade.

4. **Vitamin K's Role**:
- While vitamin K is important for the synthesis of prothrombin and other clotting factors, it is not directly involved in the conversion of prothrombin to thrombin. Instead, it helps in the production of prothrombin in the liver.

5. **Final Conversion**:
- The thrombokinase enzyme complex converts prothrombin into thrombin, which then goes on to convert fibrinogen into fibrin, forming the mesh that constitutes the blood clot.

### Conclusion:
The correct answer to the question "Conversion of prothrombin to thrombin during clotting requires" is **thrombokinase**.

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