Chromozym PL is a chromogenic substrate for plasmin, and the enzymatic reaction can be carried out in 0.1mL Tris-HCl buffer (50 mM, pH 7.8) . 100 μM Chromozym PL was dissolved and prepared. After adding the hydrolase, the generation of p-nitroaniline (pNA) at 405 nm was continuously observed, and the hydrolysis products were calculated[1].