POSSIBLE ACTION OF HUMAN PLACENTAL AMINOPEPTIDASE-N IN FETOPLACENTAL UNIT

Aminopeptidase N purified from human placenta actively hydrolyzed vari ous immunomodulating peptides from their N-terminus such as splenopent in, thymopentin, thymic humoral factor gamma 2, tuftsin and rigin in v itro. Aminopeptidase N also actively hydrolyzed neuropeptide hormones (met-enkephalin, somatostatin and neurokinin A) and vasoactive peptide s (lysyl-bradykinin and angiotensin III) from their N-terminus. In add ition, angiotensin II, secretin, thymopoietin II peptide fragment, mot ilin, endothelin-I and insulin were tested for hydrolysis by aminopept idase N. K-m and V-max values for the N-terminal amino acid, Thr, a li beration from tuftsin were 267 mu M and 8.33 mu mol/min /mg protein, r espectively. L-Leucyl-p-nitroanilidase activity in the human placental membrane fraction was almost completely neutralized by anti-aminopept idase N antibody. Our present study suggests that possible roles for s urface enzyme aminopeptidase N in the human placenta would be to down- regulate the action of immunomodulating peptides as well as vasoactive and neutopeptide hormones, and to control both immunology and endocri nology of pregnancy.