ACID INACTIVATION OF AND INCORPORATION OF PHOSPHATE INTO ALKALINE PHOSPHATASE FROM ESCHERICHIA COLI.

1. Alkaline phosphatase of Escherichia coli undergoes below pH 6.0 a reversible acid inactivation that has been studied and related to the extent of uptake of inorganic phosphate occurring below pH 6.0. 2. The rate of inactivation is rapid in the first few minutes but later it decreases markedly. Temperature, pH, composition of buffer and other factors have an important effect on the inactivation. 3. About 60% of the activity lost at pH values above 3.5 is rapidly recovered when the enzyme is taken back to pH 8.0, independently (within certain limits) of the extent of the inactivation. 4. Phosphate and Zn(2+), although very good protectors of the inactivation by acid, are not by themselves able to reverse the acid inactivation. 5. Inorganic phosphate seems not to be incorporated into the acid-inactivated enzyme. 6. Incorporation of more than one mole of phosphate/mole of enzyme has been obtained, but the phosphate residues seem to be incorporated to serine residues with a common sequence, suggesting two identical active serine residues/molecule of active enzyme.