Molecular Weight: 504.28 Salt Form: TFA Purity: >96% Sequence (3-letter): D-Ile-Pro-Arg-pNA Sequence (1-letter): iPR-pNA Storage: -20 ?C or below D-Ile-Pro-Arg-pNA is a chromogenic substrate for tissue plasminogen-activator (tPA), a serine protease found on endothelial cells lining blood vessels. tPA is the major enzyme responsible for clot breakdown by converting plasminogen to plasmin. Activity is quantified by the release of p-nitroaniline which is measured by absorbance at 405 nm.