Murein-degrading enzyme. May play a role in recycling of muropeptides during cell elongation and/or cell division. Degrades murein glycan strands and insoluble, high-molecular weight murein sacculi. Exolytic cleavage of the (1->4)-beta-glycosidic linkage between N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) residues in peptidoglycan, from either the reducing or the non-reducing ends of the peptidoglycan chains, with concomitant formation of a 1,6-anhydrobond in the MurNAc residue. Optimum pH is 4.0-4.5. Loses rapidly its activity at temperatures above 30 degrees Celsius. Forms a trimeric complex with MrcB/PonB and MipA in vitro.