Neotelomycin

The effect of neotelomycin derivatives on the cells of Bac. megaterium was studied. Derivatives with modification of one of the two active centers of the antibiotic molecule, i.e. the free alpha-amine group of the residue of asparaginic acid or hydrophobic triptophanic structure were studied. The derivative with modified indol rings of the residues of beta-methyl-and dehydrotriptophane induced the same though lower damages as the natural antibiotic: increased permeability of the cytoplasmic membranes, protoplast lysis, suppression of the dehydrogenase activity. The activity of this derivative was due to the free amino group and amounted approximately to 3 per cent of the activity of neotelomycin. The derivative with the free amino group of the asparaginic acid residue replaced by the benzoylic group showed a high antibacterial activity but had almost no effect on the membrane permeability and a very low lytic effect. The capacity of this derivative to inhibit the bacterial dehydrogenase activity remained relatively high. Possibly the free amino group of the asparaginic acid residue provided neotelomycin with the capacity for damaging the structure of the bacterial cytoplasmic membranes. No detectable damages in the membrane state after exposure to the benzoylic derivative, as well as its high antibacterial activity are evident of the fact that the mechanism of action of the benzoylic derivative on the cells was in principal different from that of the derivative preserving the free amino group. The triptophane structure was probably not only the center actively affecting the cell but also the factor that provided the antibiotic molecule with conformation most favourable for the action of the free amino group on the membrane structures.

Neotelomycin induced lysis of the protoplasts of Bac. megaterium and inhibited their succinate dehydrogenase activity. Direct correlation between the lytic activity of the antibiotic and its effect on succinate dehydrogenase was found. Neotelomycin had no effect on the dehydrogenase activity of the protoplast lysates. Possibly, suppression of the protoplast succinate dehydrogenase of Bac. megaterium under the effect of neotelomycin was due to significant structural changes caused by the antibiotic in the protoplast membranes and leading to their lysis and not to the direct effect on the enzyme. Neotelomycin had practically no effect on the spheroplast dehydrogenase activity of E. coli resistant to the antibiotic and did not induce their lysis. Resistance of E. coli to neotelomycin must be associated not with the presence of the antibiotic non-permeable cell wall but the peculiar properties of the membrane cytoplasm.