4.3.1. Extraction with Nonionic Detergent *n*-Octylpolyoxyethylene (POE)

Cell envelope pellet (6.4 mg) was resuspended in 5 mL 20 mM Tris-HCl, pH 7.4 (buffer A), containing 0.5% (*v*/*v*) POE incubated subsequently at 37 ◦C for 1 h and at 4 ◦C overnight, and then centrifuged at 25,000× *g* for 1 h. This procedure was repeated three times. The pellet was washed once with buffer A by centrifugation. The residual pellet was extracted consistently three times with 3 mL of buffer A, containing 0.5, 1, and 2% (*v*/*v*) POE. According to the SDS-PAGE data the abundant quantity of 35 kDa protein (MPOmp) was found in supernatant after extraction with 0.5% POE. Three 0.5% POE extracts were combined, concentrated to the protein content of 0.5 mg/mL, and subjected to dialysis against a 10-fold volume of buffer A, containing 0.2% POE and then purified by gel permeation chromatography on Sephacryl S-300 (Serva, Heidelberg, Germany).
