ZINC-ION-DEPENDENT ACID-PHOSPHATASE EXHIBITS MAGNESIUM-ION-DEPENDENT MYO-INOSITOL-1-PHOSPHATASE ACTIVITY

We have purified bovine brain Zn2+-dependent acid phosphatase (Zn2+-AP ase), which requires Zn2+ ions to hydrolyze the substrate p-nitropheny l phosphate (pNPP) in an acidic environment. The substrate specificity and metal requirement of Zn2+-APase at a physiological pH was also st udied. The enzyme exhibited hydrolytic activity on myo-inositol-1- and -2-monophosphates, 2'-adenosine monophosphate, 2'-guanosine monophosp hate, and the alpha- and beta-glycerophosphates, glucose-1-phosphate, and fructose-6-phosphate in 50 mM Tris-HCl buffer (pH 7.4) in the pres ence of Mg2+ ions, but not on pNPP and phosphotyrosine. Zn2+, Mn2+ and Co2+ ions were less effective for activation, Among the above substra tes, myo-inositol-1-phosphate was the most susceptible to hydrolysis b y the enzyme in the presence of Mg2+ ions. The enzyme exhibited an opt imum pH at around 8 for myo-inositol-1-phosphate in the presence of 3 mM Mg2+ ions. The Mg2+-dependent myo-inositol-1-phosphatase activity o f the enzyme,vas significantly inhibited by Li+ ions, The Zn2+-depende nt p-nitrophenyl phosphatase activity and Mg2+-dependent myo-inositol- 1-phosphatase activity of the purified enzyme fraction exhibited simil ar behavior on Sephadex G-100 and Mono Q colomns. These findings sugge st that Zn2+-APase also exhibits Mg2+-dependent myo-inositol-1-phospha tase activity under physiological conditions.