Probably plays an important role in intracellular peptide degradation. Release of an N-terminal amino acid, Xaa, from a peptide or arylamide. Xaa is preferably Glu or Asp but may be other amino acids, including Leu, Met, His, Cys and Gln. Binds 2 manganese ions per subunit. Homohexamer. Belongs to the peptidase M17 family.