| The blood-clotting proteins circulate in the blood in their inactive, proenzyme form. |
| Protein digestion begins in the stomach, where a proenzyme called pepsinogen is secreted, autocatalytically converted to Pepsin A, and used for the first step of proteolysis. |
| The fibrinolytic system involves a series of enzymatic reactions that results in the conversion of the proenzyme, plasminogen, into the trypsin-like lyric enzyme, plasmin. |
| The next to last step in this chain is the activation of the circulating proenzyme prothrombin into its active form, thrombin. |
| Degradation of fibrin clots is the function of plasmin, a serine protease that circulates as the inactive proenzyme, plasminogen. |
| The assay consists of a colorless substrate and a proenzyme extracted from amoebocyte cells in the blood of horseshoe crabs. |
