N-p-Tosyl-Gly-Pro-Lys-pNA is a colorimetric substrate for plasmin.1,2,3Plasmin binds and hydrolyzes N-p-tosyl-Gly-Pro-Lys-pNA to releasep-nitroanilide (pNA), which can be quantified by colorimetric detection at 405 nm as a measure of plasmin activity.