thrombin   works as a proteolytic enzyme to disconnects the peptides to form Fibrinogen molecule ⇒ fibrin    .  apart agent which helps in  blockage of discharging of blood also  noted as thrombus , when excessive of blood flow take place then thrombolplastin operates the establishment of enzymes which inactivates heparin and mollify it  and also adapts the inactive plasma protein into active mode ( thrombin ) .
Thrombin is an enzyme which converts fibrinogen into fibrin. The prothrombin is an inactive form of the enzyme thrombin. During clotting process, thrombinkase first converts prothrombin into thrombin and then thrombin fibrinogen into fibrin which forms a clot at the site of injury by trapping the blood cells.