The binding and secretion of alkaline phosphatase byPseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa synthesizes an inducible periplasm-located alkaline phosphatase (APase) in inorganic phosphate (Pi)-limiting medium [1]. The enzyme is released to the medium during growth [2] and it is localized both in the periplasm and on the outer surface of the cell as judged by electron microscopy [3]. The enzyme was purified to homogeneity and shown to be a dimer [4]. The native dimer is resistant to heat and proteolysis [4] and is dissociated by acid pH (pH 5.0) whereas the monomer is unstable to heat and is sensitive to trypsin digestion [3]. The enzyme is released completely from whole cells after suspension into 0.2 M MgC1 a and a fractional amount is released by suspension into 20% sucrose [1]. The present study was undertaken to demonstrate that during growth the pH of the medium decreases resulting in the inactivation of cell-free and surface bound APase whereas periplasmlocated APase is not affected. The decreased pH of the medium induces permeability changes in the outer cell wall which result in the complete release of APase after sucrose suspension. The permeability change of the outer cell wall is pH dependent and reversible. Finally, the quantity of periplasmlocated APase remains constant during growth of P. aeruginosa.