Notes: Suc-Ala-Ala-Ala-pNA is a colorimetric substrate for elastase.{66130,66131} Elastase binds and hydrolyzes Suc-Ala-Ala-Ala-pNA to release p-nitroanilide (pNA), which can be quantified by colorimetric detection at 405 nm as a measure of elastase activity.