D-Val-Leu-Lys-pNA is a colorimetric substrate for plasmin.1,2 Plasmin binds and hydrolyzes D-Val-Leu-Lys-pNA to release p-nitroanilide (pNA), which can be quantified by colorimetric detection at 405 nm as a measure of plasmin activity.
References:
[1]. Gohda, K., Fujimori, K., Teno, N., et al.Synthetic substrates specific to activated plasmin can monitor the enzymatic functional status in situ in breast cancer cellsChem. Biol. Drug Des.83(1)52-57(2014).
[2]. Leite, J.A.S., Montoya, C.A., Loveday, S.M., et al.Heat-treatments affect protease activities and peptide profiles of ruminants' milkFront. Nutr.8626475(2021).