H-D-Val-Leu-Lys-pNA . 2HCl

D-Val-Leu-Lys-p-nitroanilide is a selective colorimetric substrate for plasmin used to determine the formation of plasmin from plasminogen in amidolytic activity assays and plasminogen activating assays. Plasmin is a plasma serine protease whose main role is to dissolve fibrin blood clots. After cleavage by plasmin the protease activity is quantified by the release of p-nitroaniline (pNA) from the substrate. The rate of pNA formation, e.g. the increase in absorbance per second at 405 nm, is proportional to the enzymatic activity.