Cytosol aminopeptidases belong to the peptidase M17 family and are involved in the processing and regular turnover of intracellular proteins. Aminopeptidases catalyze the removal of the unsubstituted N-terminal amino acid from various proteins and small peptides. They are widely distributed among prokaryotes and eukaryotes and typically are hexameric enzymes. In known cases each of six subunits contains two Zn2+/Mn 2+ ions in the active site, which are fundamental for catalytic activity and exhibit different metal ion exchange kinetics. In the apo form structure subunits that form the hexamer contain two domains with mixed α/β structure that are linked by a long α-helix. The loop (residues 258-269) which forms the part of the active site is disordered and there are no Zn2+/Mn 2+ ions found in the present structure.