Evidence for the Presence of N-unsubstituted Glucosamine Residues in the Peptidoglycan of Sarcobium cytolyticum — an Intracellular Bacterial Parasite of Amoebae

Summary The chemical structure of peptidoglycan of the cell wall of Sarcobium cytolyticum , an intracellular bacterial parasite of small amoebae, was investigated. The bag-shaped peptidoglycan was isolated from intact cells by a procedure involving treatments with sodium dodecyl sulfate and digestion with pronase. The final preparation was virtually free from proteins and neutral sugars. Hydrolysis of peptidoglycan with 4 N HCl at 100°C for 12 hours yielded, in addition to glucosamine, muramic acid, alanine, diaminopimelic acid, glutamic acid and glycine (molar ratiios 0.4 : 0.4 : 1.4 : 1 : 1 : 0.3), significant amounts of a disaccharide composed of glucosaminyl-β (1–4) muramic acid. Peptidoglycan peracetylated with acetic anhydride produced on acid hydrolysis only monomeric subunits represented by glucosamine, muramic acid, alanine, diaminopimelic acid, glutamic acid and glycine in a molar ratio of 1 : 1 : 1.4 : 1 : 1 : 0.3. Estimation of free NH 2 groups in the native peptidoglycan by dinitrophenylation revealed that about 80% of the glucosamine residues were not substituted by acetyl groups and that only 44% of the diaminopimelic acid residues were involved in cross-linkage of peptide subunits. N-acetylation of peptidoglycan did not completely restore its sensitivity to the hydrolytic action of egg white lysozyme.