The rigid matrix of bacterial-cell walls - a citation classic commentary on the use of bacteriolytic enzymes in determination of wall structure and their role in cell-metabolism by Ghuyssen,J.M

The bacterial wall peptidoglycan is a network structure. Glycan strands of alternate 3,1-4 linked N-ace-tylglucosamine and N-acetylmuramic acid pyranoside residues are substituted through the D-lactyl group of N-acetylmuramic acid by L-Ala-γ-D-Glu-L-Xaa3-D-Ala peptide units where L-Xaa3 is most often a diamino acid, occasionally a neutral amino acid. Peptide units substituting adjacent glycan strands are linked together by means of bridges that involve the carboxyl group of the terminal D-Ala of one peptide and either the ω-amino group or the diamino acid L-Xaa3 or the α-carboxyl group of D-Glu of another peptide. Depending on the composition and location of the bridges, the wall peptidoglycans fall into four main chemotypes.