13 Peptydoglikan

(a) jY-Acetylglucosamine A^r-Acetylmuramic acid

Figurę 11-26 <lumk.il structuro »f peptidoglycan. (a) Ilie repeating unit of peptidoglycan is an NAG-NAM disaccharidc whose lactyl side chain forms an amide bond with a tctrapcptidc. Ilie tctrapcptidc of S. aureus is shown.Ilie isoglutamatc is so designatcd bccausc it forms an amide link via its -y-carboxyI group. In somc specics. its u-carboxylate group is replaccd by an amide group to form D-isoglutaminc and/or the l-Lvs rcsiduc may have a carboxyl group appcndcd to its C_e to form dianiiiiopimdic acid. (b) Ilie S. aureus bactcrial ccii wali peptidoglycan. In other gram-positivc bacteria. the Gly_s connecting bridges shown herc may contain different amino acid residues such as Ala or Ser. In gram-ncgativc bacteria. the peptide chains arc dircctly linked via peptide bonds.