[Membrane activity of a cell-free filtrate of Shigella flexneri 2a]

In the course of metabolism in Shigella Flexneri 2A strain there was noted secretion of a membrane-tropic factor into media. This factor increased the conductivity of bilayer lipid membranes causing formation of ionic channels in them. Minimal conductivity of the channels was about 25 pS in 0.5 M NaCl; at PH 7-8 the channels exhibited cation-anion selectivity. The calculated number of cation transfer (T+) was elevated with an increase in the channel amplitude, approaching 0.86. Since the conductivity of the channels depended on the definite potential, the component studied appears to have an intracellular localization under normal conditions; possible mechanism of its liberation into surrounding medium is discussed.