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Cell envelope protection of alkaline phosphatase against acid denaturation in Escherichia coli

The effects of a highly acidic environment on the cell-associated alkaline phosphatase activities of a smooth and a rough strain of Escherichia coli O8 have been examined. The observation that cell-associated enzyme is denatured to a lesser degree than purified enzyme suggests that the association of the enzyme with the cell envelope affords it some degree of protection from potentially disruptive agents in the environment. The degree of protection afforded the enzyme from pH denaturation appears to be dependent upon the presence of a complete lipopolysaccharide in the outer membrane of these strains. An abbreviation of the chemical structure of this cell envelope component produces a change in the outer membrane, resulting in increased susceptibility of the cells to a battery of antibiotics and to lysozyme and in a small, but significant, change in the sensitivity of the cell envelope-associated alkaline phosphatase to the denaturing effect of an acidic environment.