Effect of metal ions on the activity of green crab (Scylla serrata) alkaline phosphatase

Green crab (Scylla serrata) alkaline phosphatase (EC 3.1.3.1) is a metalloenzyme, which catalyzes the nonspecific hydrolysis of phosphate monoesters. The present paper deals with the study of the effect of some kinds of metal ions on the enzyme. The positive monovalent alkali metal ions (Li+, Na+ and K+) have no effect on the enzyme; positive bivalent alkaline-earth metal ions (Mg2+, Ca2+ and Ba2+) and transition metal ions (Mn2+, Co2+, Ni2+ and Cd2+) activate the enzyme; heavy metal ions (Hg2+, Ag+, Bi2+, Cu2+ and Zn2+) inhibit the enzyme. The activation of magnesium ion on the enzyme appears to be a partial noncompetitive type. The kinetic model has been set up and a new plot to determine the activation constant of Mg2+ was put forward. From the plot, we can easily determine the activation constant (Ka) value and the activation ratio of Mg2+ on the enzyme. The inhibition effects of Cu2+ and Hg2+ on the enzyme are of noncompetitive type. The inhibition constants have been determined. The inhibition effect of Hg2+ is stronger than that of Cu2+.