Purification and characterization of LPS‐free porins isolated from Salmonella minnesota

Abstract Porins of Salmonella minnesota , R595, were purified by anion exchange chromatography and subsequently isolated in their monomeric form by chromatofocusing. Two forms of porin could be isolated, both with an apparent molecular mass of 37 000, but of differing isolelectric points (p I 4.6 versus p I of 4.9). Porins with p I 4.9 did not contain any detectable LPS, but porins with p I 4.6 were found to contain trace amounts of LPS (1.3 × 10 −4 μg LPS/1 μg porin) as measured using a highly sensitive limulus assay. Unlike the LPS-associated porins the monomeric porins were biologically inert with regard to pore formation, but they were still able to bind C1q, a subcomponent of the first component of complement.