A readily soluble, specific and sensitive substrate for chymotrypsin and human pancreatic elastase. It is also hydrolyzed by cathepsin G and chymase. Furthermore it is the standard substrate for FK-506 binding proteins (FKBPs, also called macrophilins) and cyclophilins, which belong to the group of peptidyl prolyl cis-trans isomerases (PPIases). Thus, Suc-AAPF-pNA has been used for an uncoupled protease-free assay of PPIase activity.