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  • Title: Inhibitory effect of magnesium ion on the human placental alkaline phosphatase-catalyzed reaction in a reverse micellar system.
    Author: Hung HC, Huang TM, Chang GG.
    Journal: J Protein Chem; 1998 Feb; 17(2):99-106. PubMed ID: 9535271.
    Abstract:
    Human placental alkaline phosphatase is a membrane-anchored protein. Entrapping the enzyme into a reverse micellar vesicle mimics the in vivo conditions and allows examination of the properties of the enzyme. Placental alkaline phosphatase is enzymatically active in Aerosol-OT/isooctane reverse micelles. Substantially different kinetic behavior of the enzyme has been observed in aqueous or reverse micellar systems. In aqueous solution, Mg2+ is a nonessential activator of the enzyme. In the experiments described in the present report Mg2+ was found to be an inhibitor for the enzyme in reverse micelles. This inhibition is presumably due to a time-dependent conformational change of the enzyme molecule, which resulted in a curvature in the recorder tracings of the enzyme assays. The Mg2+-induced conformational change of the enzyme was completely prevented by phosphate and partially reserved by EDTA. High concentrations of Zn2+ also strongly inhibited enzyme activity in both aqueous and reverse micellar solvent systems, presumably by occupying the Mg2+ (M3) site of the enzyme. However, binding of Zn2+ at the M3 site did not cause conformational change of the enzyme and the enzyme assay tracing was linear. The M3 site of the enzyme is proposed to have a modulatory role in vivo using magnesium ion as the modulator.
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