Adsorption of 14C-labeled gramicidin S on cell of bacteria

Gramicidin S (GS) containing 14C-labeled proline was synthesized by a solid-phase method, and the labeled GS dihydrochloride was obtained as crystals. The labeled GS exhibited same antibacterial activity as natural GS. Strains sensitive to GS (B. subtilis and S. aureus) and an insensitive strain (E. coli) were treated with the labeled GS, and the amount of the labeled GS adsorbed on the cells was measured. GS was adsorbed rapidly on the cells of the sensitive strains; the amount adsorbed increased linearly with GS concentration up to 1-1.5 microgram/ml, and at a lower rate at above 1.5 microgram/ml. GS molecules covered most of the cell surface at the minimum inhibitory concentration of 1.5 microgram/ml; the number of molecules adsorbed per cell was 1.3-1.4 x 10(6). No GS was adsorbed by the insensitive strain.