Murein-degrading enzyme. May play a role in recycling of muropeptides during cell elongation and/or cell division. Preferentially cleaves at a distance of more than two disaccharide units from the ends of the glycan chain. Prefers cross-linked murein in vivo. Endolytic cleavage of the (1->4)-beta-glycosidic linkage between N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) residues in peptidoglycan with concomitant formation of a 1,6-anhydrobond in the MurNAc residue. The N-terminus is blocked. Belongs to the transglycosylase Slt family.