OUTER MEMBRANE OF SALMONELLA-TYPHIMURIUM .10. IDENTIFICATION OF PROTEINS EXPOSED ON CELL-SURFACE

Proteins exposed on the outer surface of the outer membrane of S. typhimurium were identified by reacting intact cells with a covalent labeling reagent. Since the outer membrane permitted the free diffusion of small hydrophilic molecules, a macromolecular reagent, CNBr-activated dextran, was used as the non-penetrating labeling agent. A mutant producing a lipopolysaccharide with a short (i.e., hexasaccharide) carbohydrate chain was used to avoid steric hindrance by the carbohydrates on the membrane surface. Of the 4 major proteins of MW .apprx. 35,000, 3 were exposed, and at least 6 other proteins were exposed on the cell surface. Only 2 or 3 outer membrane proteins consistently did not react with the reagent in intact cells.