Involved in muropeptide recycling. Hydrolyzes the amide bond between N-acetylmuramic acid (MurNAc) and the L-alanine residue of the stem peptide. Cannot hydrolyze muropeptides containing N-acetylglucosamine (GlcNAc) at the non-reducing end. Hydrolyzes the link between N-acetylmuramoyl residues and L-amino acid residues in certain cell-wall glycopeptides. Cell wall biogenesis; peptidoglycan recycling. Belongs to the peptidase S12 family. Truncated N-terminus.