Cell surface-localized alkaline phosphatase of Escherichia coli as visualized by reaction product deposition and ferritin-labeled antibodies

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Abstract
When cells of a wild-type E. coli O8 strain bearing a complete lipopolysaccharide were incubated for alkaline phosphatase [EC 3.1.3.1] reaction product and examined by EM, the deposition of Pb salts was observed primarily within the periplasmic space. A similar treatment of cells derived from this strain, which bears a highly abbreviated lipopolysaccharide, showed a mixed cell surface and periplasmic localization of reaction product, suggesting a surface association of a portion of the enzyme. To further explore this possibility, ferritin-[rabbit]antibody conjugates against the active enzyme and its irreversibly dissociated subunits were prepared and allowed to react with cells of both strains. The presence of active enzyme and inactive subunits of the enzyme at the cell surface of the mutant strain was demonstrated. The validity of the reaction product deposition technique was thus substantiated, and apparently alkaline phosphatase may be associated with some component of the outer membrane in this organism. The observation of enzyme subunits at the cell surface further suggests that an association of these subunits with structural components of the cell envelope may provide a locus at which they may dimerize to form active enzyme.