Cleaves the N-terminal amino acid of tripeptides. Release of the N-terminal residue from a tripeptide. Binds 2 Zn(2+) ions per subunit. kcat is 639 sec(-1) with GGF tripeptide as substrate. kcat is 915 sec(-1) with GGA tripeptide as substrate. kcat is 1015 sec(-1) with GAA tripeptide as substrate. kcat is 1219 sec(-1) with GAY tripeptide as substrate. kcat is 373 sec(-1) with AAA tripeptide as substrate. kcat is 1640 sec(-1) with AAG tripeptide as substrate. Optimum pH is around 8. Optimum temperature is slightly lower than 40 degrees Celsius. Belongs to the peptidase M20B family.