Résumé
The two side chain amino groups of the two L-ornithine residues in gramicidin-S seem to be important for the antibacterial activity of the molecule, since complete acetylation, formylation, carbamylation, deamination, trinitrophenylation, succinylation, maleylation of the antibiotic caused 90–95 % loss of the antibacterial activity of the antibiotic. However this modification leads to only 12–30% loss of the hemolytic activity. Monoacetyl- and monoformyl gramicidin-S with a free amino group retains nearly 50% of the antibacterial activity of the molecule. It seems, therefore, that the two amino groups contribute equally to the antibacterial activity of gramicidin-S.
Résumé
The single imidazole nucleus of L-histidine residue in bacitracin-A seems to be important for the anti-bacterial activity of the molecule, since iodination, carboxymethylation and coupling of diazobenzene sulphonic acid to the histidine residue in the antibiotic caused 90-94% loss of antibacterial activity of the antibiotic. In contrast, the bacitracin sulphone and sulphoxide derivatives are as active as the parent antibiotic.
Résumé
The single side chain amino group of the D-ornithine residue in bacitracin seems to be important for the antibacterial activity of the molecule, since, acetylation, formylation, carbamylation and deamination of the antibiotic caused 90-92% loss of antibacterial activity. In contrast, nearly 80-91% of the antibacterial activity of the parent antibiotic was retained after the esterification, amide formation and acid-chloride formation of the a - and Υ –carboxyl groups of D-asparagine and D-glutamic acid residues of the antibiotic, respectively.