Zinc-Ion-Dependent Acid Phosphatase Exhibits Magnesium-Ion-Dependent myo-Inositol-1-phosphatase Activity

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We have purified bovine brain Zn^<2+>-dependent acid phosphatase (Zn^<2+>-APase), which requires Zn^<2+> ions to hydrolyze the substrate p-nitrophenyl phosphate (pNPP) in an acidic environment. The substrate specificity and metal requirement of Zn^<2+>-APase at a physiological pH was also studied. The enzyme exhibited hydrolytic activity on myo-inositol-1-and-2-monophosphates, 2'-adenosine monophosphate, 2'-guanosine monophosphate, and the α- and β-glycerophosphates, glucose-1-phosphate, and fructose-6-phosphate in 50 mM Tris-HCl buffer (pH 7.4) in the presence of Mg^<2+> ions, but not on pNPP and phosphotyrosine. Zn^<2+>, Mn^<2+> and Co^<2+> ions were less effective for activation. Among the above substrates, myo-inositol-1-phosphate was the most susceptible to hydrolysis by the enzyme in the presence of Mg^<2+> ions. The enzyme exhibited an optimum pH at around 8 for myo-inositol-1-phosphate in the presence of 3 mM Mg^<2+> ions. The Mg^<2+>-dependent myo-inositol-1-phosphatase activity of the enzyme was significantly inhibited by Li^+ ions. The Zn^<2+>-dependent p-nitrophenyl phosphatase activity and Mg^<2+>-dependent myo-inositol-1-phosphatase activity of the purified enzyme fraction exhibited similar behavior on Sephadex G-100 and Mono Q colomns. These findings suggest that Zn^<2+>-APase also exhibits Mg^<2+>-dependent myo-inositol-1-phosphatase activity under physiological conditions.
公益社団法人日本薬学会の論文
1996-06-15