Aminopeptidase is a plasma membrane-bound enzyme present in macrophages as well as a variety of other cells. They are widely distributed throughout the animal and plant kingdoms and are found in many subcellular organelles, cytosol, and membrane components. Aminopeptidases are used in essential cellular functions. Many, but not all, of these peptidases are zinc metalloenzymes. In human peripheral blood or bone marrow, the enzyme is present in monocytes and granulocytes but not in lymphocytes, basophils, or promyelocytes.