The cell envelope of Shigella sonnei phase I, phase II and R-form was fractionated inot outer and cytoplasmic membrane components by means of sucrose density gradient centrifugation. The protein composition of the outer membrane has been analyzed by SDS-polyacrylamide gel electrophoresis. The outer membrane preparations contained 15-17 proteins. The major proteins of the outer membrane were of apparent molecular weights: 27,000, 28,000 and 31,000. Their amount varied depending on the structural defects of lipopolysaccharide.
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