Component of the cylindrical core that assembles on the inner surface of the capsid during procapsid formation. Plays a role in ejection of the bacteriophage DNA into the host cell at the initiation of infection. Functions as an exolysin that catalyzes the cleavage of the host peptidoglycans. Hydrolysis of (1->4)-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Optimum pH is 6. The enzyme is highly thermoresistant, but not thermostable.