Identification of three porins in the outer membrane ofBacteroides fragilis

Four outer membrane proteins were purified to homogeneity from isolated outer membranes of Bacteroides fragilis; three (Mr 51000, 92000 and 125 000) had pore-forming activity in reconstituted liposomes as determined by swelling assay. Membrane vesicles containing the Mrmr 55 000 outer membrane protein showed no detectable pore-forming activity. The three B. fragilis porins formed pores that allowed the penetration of uncharged saccharides of Mr lower than 340–400, even though the efficiency of solute diffusion showed slight differences. The diffusion rates of glucose through the porins appeared to be lower than those through Escherichia coli porins.