A protein isolated and purified from the outer membrane of the acidophilic, chemolithotrophic bacterium, Thiobacillus ferrooxidans with an oligomeric molecular weight of 90 000 Da (p9O) was incorporated into phosphatidylethanolamine planar lipid bilayers. The protein formed slightly anionic channels in KCl solutions, with a conductance of 25 pS in 100 mM KCl. The current—voltage relationship was linear between ±6O mV, and the conductance was a saturating function of the salt concentration. These channels fluctuated from a single open to closed state at low potentials, but present flickering activity at higher potentials.
