ALTERATIONS IN STRUCTURE AND FUNCTION OF ESCHERICHIA COLI ALKALINE PHOSPHATASE DUE TO ZN2+ BINDING

The enzymatic activity of alkaline phosphatase from Escherichia coli increases linearly with the mole ratio, Zn2+/86,000 molecular weight of protein. There is one phosphate binding site per molecule of dimer containing from two to four bound zinc ions. The tertiary structure of alkaline phosphatase is altered by metal binding as evidenced by ultraviolet difference spectra and circular dichroism in the wavelength range 2600-3200 Å. In addition, spectrophotometric titration shows four tyrosine residues exposed to solvent in the native dimer containing three Zn2+ ions and ten such residues exposed to solvent in the metal-free apoprotein. A refolded subunit ofalkaline phosphatase obtained by neutralization of the acid-dissociated and unfolded protein has optical properties similar to those of the metal-free dimer. This subunit is capable of dimerization in the presence of chelating agent. © 1969, American Chemical Society. All rights reserved.