MICROCIN E492 FORMS ION CHANNELS IN PHOSPHOLIPID-BILAYER MEMBRANES

Microcin E492, a polypeptide antibiotic, has been shown to have an M(r ) of 6,000 by urea-SDS-polyacrylamide gel electrophoresis of the fluor escently labelled compound. It is known that the bactericidal action o f microcin involves a loss of the transmembrane potential. In this stu dy we show that microcin forms cation-selective channels in planar pho spholipid bilayers. The channels have two main conductance states the current-voltage curves of which rectify. The reversal potentials measu red under biionic conditions indicate a permeability sequence of NH4> K+ = Rb+ = Cs+ > Na+ = Li+ > Tris+. The results suggest that membran e potential dissipation induced by microcin is a consequence of the fo rmation of pores in the bacterial membrane.