MME is a type II transmembrane glycoprotein and a common acute lymphocytic leukemia antigen that is an important cell surface marker in the diagnosis of human ALL (acute lymphocytic leukemia). MME is present on leukemic cells of pre-B phenotype, which represent 85% of cases of ALL. MME is not restricted to leukemic cells, however, and is found on a variety of normal tissues. MME is a neutral endopeptidase that cleaves peptides at the amino side of hydrophobic residues and inactivates several peptide hormones including glucagon, enkephalins, substance P, neurotensin, oxytocin, and bradykinin.