Effects of certain mono-, di- and trivalent metal cations on the K+ -stimulated p-nitrophenyl phosphatase in rat brain

: The effects of certain monovalent (Ag+1 and Li+1), divalent (Hg+2, Cu+2, Zn+2, Co+2, Fe+2, Pb+2, Mn+2, Sn+2, Ni+2, and Se+2) and trivalent (Fe+3, As+3, and Al+3) metals on a mitochondrial preparation of K+-stimulated-p-nitrophenyl phosphatase (K+-PNPPase) from rat brain were studied. Except for salts of Ni+2, Se+2 and Li+1, which irrespective of concentration failed to produce 50% inhibition, all of the metals examined were found to be potent inhibitors of the enzyme with 150 values of 0.24 μM for Ag+1 among the monovalent, 0.70, 30, 37, 38, 47, 60, 62, 490 and 850μM for Hg+2, Cu+2, Cd+2, Zn+2, Co+2, Fe+2, Pb+2, Mn+2 and Sn+2, respectively, among the divalents and 100, 550 and 870 μM for Fe+3, As+3, and AL+3 respectively, among the trivalents. Salts of silver and mercury were the most toxic for this enzyme. All metals showed concentration dependent inhibition except lithium. The order of their potency was Ag+1> Hg+2> Cu+2> Cd+2> Zn+2> Co+2> Fe+2> Pb+2> Fe+3> Mn+2> As+3> Sn+2> Al+3> Ni+2> Se+2> Li+1.