Characterization of further association of the trimeric membrane protein porin by low-angle laser-light scattering photometry coupled with high-performance gel chromatography.

Porin (OmpF), a trimeric membrane protein, in an extract of the outer membrane of Escherichia coli gave a twin-peaked elution pattern on Sephacryl S-300HR gel chromatography in the presence of sodium dodecyl sulphate. The species eluting earlier and later were found to be the hexamer and trimer, respectively, from molecular mass determination by low-angle laser-light scattering photometry coupled with TSK-G3000SWXL gel chromatography. As the hexamer was dissociated into the trimer under the conditions of sodium dodecyl sulphate polyacrylamide gel electrophoresis, its presence had been overlooked. The addition of lipopolysaccharide, another component of the outer membrane, and subsequent dialysis induced association of the trimer, the product containing an appreciable amount of the hexamer.