In vivo properties of colicin A: channel activity is voltage dependent but translocation may be voltage independent.

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Abstract
The kinetics of K+ efflux caused by colicin A in Escherichia coli-sensitive cells have been investigated by using a K+-selective electrode. The order of magnitude of the rate of K+ efflux per colicin molecule was comparable to that of ion channels. The dependence of K+ efflux upon multiplicity, pH, temperature, and membrane potential (.DELTA..PSI.) was determined. The translocation of colicin A from the outer membrane receptor to the inner membrane and insertion into the inner membrane required a fluid membrane, but once inserted, the channel properties showed little dependence upon the state of the lipids. At a given multiplicity, the lag time before the onset of K+ efflux was found to reflect the time required for translocation and/or insertion of colicin into the cytoplasmic membrane. Opening of the channel only occurred above a threshold value of .DELTA..PSI. of 85 .+-. 10 and 110 .+-. 5 mV at pH 6.8 and 7.8 respectively. Conditions were designed for closing and reopening of the channel in vivo. These conditions allowed us to test separately the .DELTA..PSI. requirements for translocation and channel opening: translocation and/or insertion did not appear to require .DELTA..PSI.. The channel formed in vivo featured properties similar to that of the channel in lipid planar bilayers.