The distribution of diamino acids in cell walls of bacterial species bears some relation to taxonomy. The most widely distributed diamino acid is -diaminopimelic acid which is present in probably all Gram-negative species and in numerous other genera. L-lysine, also fairly common, is present in most Gram-positive cocci and in certain other species. Less frequent are DD or LL-diaminopimelic, β-OH - diaminopimelic, D or L ornithine, D or L diaminobutyric. The positions of these bifunctional amino acids in mucopep-tides (glycopeptides), the cross linked polymers of the walls, are described. Mucopeptides are divided into two types according to the site of termination of the cross-link from the D-alanine of an adjacent peptide chain. In type D, the site is the diamino acid which is located in the main peptide chain; in type G (less common) the site is the D-glutamic acid, and the diamino acid is in the cross link. Other differentiating features of types D and G include the optical configuration of the diamino acid, and the nature of the amino acid linking the peptide chain to the hexosamine backbone.


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