Analysis and Chemical Modification of Bacterial Porins
The cell envelope of gram-negative bacteria such as Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa consists of three different layers, the outer membrane, the peptidoglycan (murein) layer, and the inner membrane (Nikaido, 1979a; Beveridge, 1981). The inner membrane acts as a real diffusion barrier and contains, in addition to the respiration chain and the H+ -ATPase, a large number of different transport systems for substrates. The peptidoglycan or murein layer consists of repeating N-acetylglucosaminyl-N-acetylmuramyl dimers, which form a macromolecule surrounding the cell (Beveridge, 1981). This layer protects the cells from lysis. The outer membrane is a molecular filter with defined exclusion limits for hydrophilic substrates (Nikaido and Nakae, 1979). In enteric bacteria, the outer membrane acts also as a barrier for hydrophobic compounds such as detergents (Nikaido, 1979b). The active substrates of the molecular sieving properties for hydrophilic substances are a major class of proteins called matrix proteins (Rosenbusch, 1974) or porins (Nakae, 1976).
KeywordsOuter Membrane Outer Membrane Protein Lipid Bilayer Membrane Selectivity Filter General Diffusion
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