Fibroblast activation protein a (FAPa) also known as seprase belongs to type II integral membrane proteins. FAPa/seprase bounded to cell membrane is serine proteinase with gelatinase activity. Serine proteases family included among others S9B post-prolyl dipeptidyl aminopeptidase subfamily. Besides FAPa/seprase, to S9B subfamily belongs dipeptidyl peptidase IV (DPPIV). Catalytically active FAPa is a 170 kDa homodimer, consisting of two 97 kDa subunits. FAPa besides homodimers also forms heteromeric, catalytically active complexes with DPPIV.