FORMATION AND PROPERTIES OF A TETRAMERIC FORM OF ESCHERICHIA COLI ALKALINE PHOSPHATASE

Alkaline phosphatase from Escherichia coli has been studied extensively in a dimeric state containing four bound Zn2+ per dimer. It has now been shown that at free Zn2+ concentrations >10-5 M rapid and reversible selfassociation occurs between pH 7.0 and 8.0. At pH 8.0 and an equilibrium concentration of Zn2+ = 10-4 M all of the protein is present as tetramer containing 16 Zn2+/tetramer. Hydrodynamic studies show no significant alteration in shape of the tetramer compared with dimer, and optical measurements indicate that one tryptophan residue per chain is removed from contact with solvent as the result of association. There is an increase in phosphate binding with tetramerization. © 1969, American Chemical Society. All rights reserved.