This plasmin chromogenic substrate is lyophilized with 60 mg mannitol as a bulking agent. 

Formula:  H-D-Val-Leu-Lys-pNA-2HCl

The method for the determination of activity is based on the difference in absorbance between the pNA formed and the original substrate.  The rate of pNA formation, i.e. the increase in absorbance per second at 405nm, is proportional to the enzymatic activity and is determined with a spectrophotometer.