本酶催化的反应为Hydrolyses Xaa-Pro! Bonds To Release Unblocked, N-Terminal Dipeptides From Substrates Including Ala-Pro!p-Nitroanilide And (Sequentially) Tyr-Pro!Phe-Pro!Gly-Pro!Ile,来自乳酸乳球菌(Lactococcus lactis)的胞内酶(190-kDa)是肽酶家族S15的典型代表。该反应与动物的二肽基肽酶IV催化的反应相似。