Substituents on the alpha-carboxyl group of D-glutamic acid in the peptidoglycan of several bacterial cell walls

Several different carbohydrate-free peptides have been obtained from cell walls of Staphylococcus aureus and Arthrobacter crystallopoietes by degradation with lytic enzymes. They all contained one residue of amide ammonia per repeating subunit. A peptide obtained from cell walls of Micrococcus lysodeikticus contained no ammonia but had a glycine residue with a free carboxyl group.
It has been demonstrated by Edman degradation that both the amide ammonia in the former two cell walls and the COOH-terminal glycine in the latter are substituted on the α-carboxyl group of glutamic acid. Other features of the structures of these peptides are discussed.