en Microbiology and Anatomy Microbiology and Anatomy Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine Isolation and purification of major outer membrane proteins (OMP) from the cell wall envelope of Brucella abortus S-99 were achieved by sonication, solubilization and membrane fractionation in the presence of non-ionic detergent (Tx-100) and lysozyme treatments, followed by ultracentrifugation. The crude OMP was treated with trypsin to free the preparation from any other protein contaminants. The OMP preparation was purified by column chromatography on Sephacryl S-200. Three major symmetrical peaks emerged from the column with kav values of 1. 81, 2.42 and 2.56 in succession in addition to a few closely related minor peaks. Characterization of crude OMP on SDS-PAGE showed 13 protein bands. The three major peaks 1,2 and 3 were subjected to SDS-PAGE separately and the molecular weights of peaks 2 and 3 were calculated to be 26 and 38 kDa, respectively and the first peak was further resolved into two subfractions with molecular weights of 62 and 67 kDa. However, after treatment of OMP with trypsin the number of bands were reduced to one prominent band with a molecular weight of 38 kDa and a thinner band of 41 kDa. 47 51 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-496&slc_lang=en&sid=1 FERESHTEH SHAHCHERAGHI 20031947532846004915 20031947532846004915 No From the Department of Microbiology, Medical School, Tarbiat Modaress University, Tehran, MOHAMMAD BAGHER ESLAMI 20031947532846004916 20031947532846004916 No From the Department of Microbiology, Medical School, Tarbiat Modaress University, Tehran, BAHMAN TABARAIE 20031947532846004917 20031947532846004917 Yes the Department of Bacterial Vaccine and Antigen Production, Pasteur Institute of Iran, Tehran, Islamic Republic of Iran. GHORBAN BEHZADIAN-NEJAD 20031947532846004918 20031947532846004918 No From the Department of Microbiology, Medical School, Tarbiat Modaress University, Tehran,