Aminopeptidase with specificity towards an acidic amino acid at the N-terminus. Likely to play an important role in intracellular protein and peptide metabolism (By similarity). Release of an N-terminal aspartate or glutamate from a peptide, with a preference for aspartate. Binds 2 Zn(2+) ions per subunit. One of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity. Tetrahedron-shaped homododecamer built from six homodimers. Ubiquitous. Belongs to the peptidase M18 family.