title: Modifications of the acyl-D-alanyl-D-alanine terminus affecting complex-formation with vancomycin.
abstract: Vancomycin forms complexes with peptides terminating in d-alanyl-d-alanine that are analogous to the biosynthetic precursors of bacterial mucopeptides. The specificity of complex-formation has been studied by means of many synthetic peptides, prepared by both solid-phase and conventional methods. The following conclusions can be drawn: (a) three amide linkages are required to form a stable complex; (b) the terminal carboxyl group must be free; (c) the carboxyl terminal and subterminal residues must be either glycine or of the d-configuration; (d) the size of the side chain in these residues greatly influences the affinity for vancomycin, a methyl group being the optimum in each case; (e) the nature of the side chain in the third and fourth residues has a smaller effect on complex-formation, but an l-configuration was somewhat better than a d-configuration in the third position. In addition to acyl-d-alanyl-d-alanine, other peptides that occur in bacterial cell walls will combine with vancomycin, although less strongly, e.g. acyl-d-alanyl-d-alpha-amino acid (where the terminal d-residue may form the cross-link in mucopeptide structure) and acyl-l-alanyl-d-glutamylglycine (a sequence found in the mucopeptide of Micrococcus lysodeikticus and related organisms). These results throw some light on the specificity of the uptake of vancomycin by living bacteria.
mesh_terms: D000409:Alanine; D000577:Amides; D001665:Binding Sites; D002264:Carboxylic Acids; D002845:Chromatography; D004586:Electrophoresis; D005971:Glutamates; D005998:Glycine; D010455:Peptides / Q000138:chemical synthesis; D013053:Spectrophotometry; D014640:Vancomycin
chemical_list: D000577:Amides; D002264:Carboxylic Acids; D005971:Glutamates; D010455:Peptides; D014640:Vancomycin; D000409:Alanine; D005998:Glycine