The peptide antibiotic subtilin acts by formation of voltage-dependent multi-state pores in bacterial and artificial membranes.
The peptide antibiotic subtilin was shown to induce a rapid efflux of amino acids from intact bacterial cells and cytoplasmic membrane vesicles, and to prevent amino acid uptake by cells preincubated with the peptide. Upon addition of subtilin the trans-membrane potential (delta psi) was greatly reduced. Starved bacterial cells were less sensitive to subtilin than energized cells. Depolarization of cells by carbonyl cyanide m-chlorophenylhydrazone prevented subtilin action, but its activity could be restored by a valinomycin-induced potassium diffusion potential. Using this technique, we deduced a threshold potential of about -90 to -100 mV to be essential for subtilin action on intact cells. A similar value was obtained in macroscopic conductance measurements with black lipid membranes. The current-voltage characteristic was symmetric, i.e. subtilin induced membrane currents with trans-negative and trans-positive voltages. Single-channel experiments revealed short-lived multi-state pores of the alamethicin type. The pores had lifetimes of several hundred milliseconds and pore diameters of up to approximately 2 nm.