Which enzyme is responsible for the conversion of inactive fibrinogens to fibrins ?

The correct option is Thrombin.

Step-by-step explanation:
1. Blood Coagulation Cascade: When a blood vessel is injured, the body initiates a cascade of enzymatic reactions to form a clot and prevent excessive blood loss.
2. Activation of Prothrombin: During the coagulation process, the enzyme complex thrombokinase (also known as prothrombinase) converts the inactive plasma protein prothrombin into its active form, thrombin, in the presence of calcium ions.
3. Conversion of Fibrinogen to Fibrin: Once formed, active thrombin acts as a proteolytic enzyme that specifically cleaves the soluble, inactive protein fibrinogen into insoluble fibrin monomers.
4. Clot Formation: These fibrin monomers rapidly polymerize to form a network of insoluble fibrin threads. This network traps platelets and red blood cells, completing the formation of a stable blood clot.
5. Conclusion: While thrombokinase is responsible for initiating the activation of thrombin, it is thrombin itself that directly catalyzes the conversion of inactive fibrinogen to fibrin.