Cleaves the N-terminal amino acid of tripeptides. Hydrolyzes tripeptides containing N-terminal methionine, leucine, or phenylalanine. Displays little or no activity against dipeptides, N-blocked or C-blocked tripeptides, and tetrapeptides. Release of the N-terminal residue from a tripeptide. Binds 2 Zn(2+) ions per subunit. Inhibited by EDTA. Homodimer. Belongs to the peptidase M20B family.