Expression of the phoA gene cloned in a multicopy plasmid in Escherichia coli E15 (ΔphoA) results in overproduction of the alkaline phosphatase. Secretion occurs into the periplasm and the culture medium, and accumulation of a precursor (prePhoA) occurs as insoluble aggregates. All these forms of the enzyme were purified and their properties were studied. Extracellular and periplasmic enzymes differ in V(max) and K(m) values but have similar activation energies (E(a)). Mature alkaline phosphatase and intermediate forms can be isolated from one E. coli culture.
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