γ‐Glutamyl‐glutamic Acid, an Interpeptide Bridge in the Murein of Some Micrococci and Arthrobacter sp.

The mureins of several micrococci and coryneform organisms contain more than one mole of glutamic acid per mole of meso‐diaminopimelic acid (Dpm). The amino acid sequence of these mureins was studied. The peptide subunit consists of Mur‐l‐Ala‐γ‐d‐Glu‐meso‐Dpm‐d‐Ala, where Mur = muramic acid. The γ‐carboxyl group of glutamic acid is substituted in most cases by a glycine amide. The cross‐linkage of the peptide subunits is performed by the dipeptide γ‐d‐glutamyl‐d‐glutamic acid. This peptide is bound by the γ‐carboxyl group of the C‐terminal glutamic acid to the amino group of diaminopimelic acid and to the carboxyl group of d‐alanine of an adjacent peptide subunit by the amino group of the N‐terminal glutamic acid. The mureins of the micrococci studied contain only one mole of amide ammonia per mole of diaminopimelic acid and this is bound to glycine. In the mureins of the coryneform organisms a second mole of amide ammonia was found which is probably bound to diaminopimelic acid. The murein of Staphylococcus lactis CCM 2432 lacks amide ammonia as well as glycine.