Mechanism of action of Mg2+ and Zn2+ on rat placental alkaline phosphatase. I. Studies on the soluble Zn2+ and Mg2+ alkaline phosphatases.
Rat placental alkaline phosphatase (EC 3.1.3.1), a dimer of 135,000 daltons, is strongly activated by Mg2+. However, Zn2+ has to be present on the apoenzyme to obtain this activation. Mg2+ alone is unable to reconstitute functional active sites. Excess Zn2+ which competes for the Mg2+ site leads to a phosphatase with little catalytic activity at alkaline pH but with normal active sites at acidic pH as shown by covalent incorporation of ortho-[32P]phosphate. Two enzyme species with identical functional active sites have been reconstituted that only differ by the presence of Zn2+ or Mg2+ at the effector site. A mechanism is presented by which alkaline phosphatase activity of rat placenta would be controlled by a molecular process involving the interaction of Mg2+ and Zn2+ with the dimeric enzyme molecule.
D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002614:Chelating Agents / Q000494:pharmacology; D003956:Dialysis; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011485:Protein Binding; D051381:Rats; D015032:Zinc / Q000494:pharmacology*
D002614:Chelating Agents; D046911:Macromolecular Substances; D010710:Phosphates; D000469:Alkaline Phosphatase; D008274:Magnesium; D015032:Zinc