Cleaves the N-terminal amino acid of tripeptides. Shows broad substrate specificity, exhibiting maximum activity against hydrophobic tripeptides, with the highest activity for Met-Gly-Gly. Therefore this enzyme may play an important role in flavor formation during cheese ripening. Is also able to slowly hydrolyze some hydrophobic dipeptides, but displays no activity against tetrapeptides and the tripeptide Phe-Gly-Gly. Release of the N-terminal residue from a tripeptide. Binds 2 Zn(2+) ions per subunit. Totally inhibited by EDTA, EGTA, and 1,10-phenanthroline. Strongly inhibited by divalent cations such as Cu(2+), Cd(2+), Co(2+) and Mn(2+). Partially inhibited by the reducing agents 2-mercaptoethanol and dithiothreitol. Optimum pH is 7.5. Highly active from pH 6 to 8. Optimum temperature is 25-37 degrees Celsius. Thermolabile. Approximately 45% of the activity remains after incubation for 15 min at 45 degrees Celsius. Homotrimer. Belongs to the peptidase M20B family.