title: Voltage-dependent, monomeric channel activity of colicin E1 in artificial membrane vesicles.
abstract: The dependence of colicin channel activity on membrane potential and peptide concentration was studied in large unilamellar vesicles using colicin E1, its COOH-terminal thermolytic peptide and other channel-forming colicins. Channel activity was assayed by release of vesicle-entrapped chloride, and could be detected at a peptide: lipid molar ratio as low as 10(-7). The channel activity was dependent on the magnitude of a transnegative potassium diffusion potential, with larger potentials yielding faster rates of solute efflux. For membrane potentials greater than -60 mV (K+in/K+out greater than or equal to 10), addition of valinomycin resulted in a 10-fold increase in the rate of Cl- efflux. A delay in Cl-efflux observed when the peptide was added to vesicles in the presence of a membrane potential implied a potential-independent binding-insertion mechanism. The initial rate of Cl- efflux was about 1% of the single-channel conductance, implying that only a small fraction of channels were initially open, due to the delay or latency of channel formation known to occur in planar bilayers. The amount of Cl- released as a function of added peptide increased monotonically to a concentration of 0.7 ng peptide/ml, corresponding to release of 75% of the entrapped chloride. It was estimated from this high activity and consideration of vesicle number that 50-100% of the peptide molecules were active. The dependence of the initial rate of Cl- efflux on peptide concentration was linear to approximately the same concentration, implying that the active channel consists of a monomeric unit.
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D003087:Colicins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D008567:Membranes, Artificial; D009994:Osmolar Concentration; D014634:Valinomycin / Q000378:metabolism
chemical_list: D002712:Chlorides; D003087:Colicins; D007473:Ion Channels; D008567:Membranes, Artificial; D014634:Valinomycin; D002118:Calcium