Suc-Ala-Phe-Pro-Phe-pNA, 128802-73-3, C36H40N6O9, Mr 700.75, 50mg. Substrate for FK-506 binding proteins (FKBPs, also called macrophilins) and cyclophilins, which belong to the group of peptidyl prolyl cis-trans isomerases (PPIases). Suc-AFPF-pNA has been used for an uncoupled protease-free assay of PPIase activity.