FIG. 1.

ColE2 preincubated with sensitive cells inhibits reception of group A colicins. (A) Initial rate of K⁺ efflux induced by various colicins at various multiplicities (number of colicin molecules per cell). Cells (2 × 10⁹ per ml) were incubated at 37°C in sodium phosphate buffer (100 mM [pH 7.2]) containing 0.2% glucose and 0.5 mM KCl. Colicins A (diamonds), B (triangles), E1 (squares), and E2 (circles) were added at time zero. The initial rates were measured in the linear part of the efflux curves. (B) Effect of colicin E2 on the activities of group A and B colicins. Colicin E2 was added to the cells at various multiplicities at time zero. Colicins A (diamonds), E1 (squares), and B (triangles) were added at a multiplicity of 200 5 min after introduction of colicin E2. The initial rates were measured and correlated to the numbers of colicin molecules reaching their targets. The percentage of inhibition was calculated as described in Materials and Methods. (C) Colicin E2 was added to the cells at the multiplicity of 800 at time zero. Colicin A was added at a multiplicity of 200 at various times after introduction of colicin E2. The initial rates were measured and correlated to the number of colicin molecules reaching their targets. The percentage of inhibition was calculated as described in Materials and Methods. Each experiment was performed in triplicate.