Inhibitory effect of zinc and copper on phosphatase activity in the brain cytosol of rats: Involvement of SH groups

Abstract

The effect of various metal ions on neutral phosphatase activity in the brain cytosol of rats was investigated. p-Nitrophenylphosphate was used as the substrate for the enzyme assay. Brain cytosolic phosphatase activity was significantly decreased by the presence of zinc or copper in the range of 10-5 to 10-3M in the enzyme reaction mixture, while it was significantly increased by manganese, nickel or cobalt (10-5 to 10-3 M). Calcium (10-5 to 10-3 M) did not have an appreciable effect on brain cytosolic phosphatase activity. The inhibitory effect of zinc (10-5 M) or copper (10-5 M) on phosphatase activity was seen in the presence of manganese, nickel or cobalt with 10-4M concentration, indicating a potent inhibitory effect of these metals. Zinc or copper-decreased phosphatase activity was clearly prevented by dithiothreitol (5 mM), although the effect of each metal was further enhanced by N-ethylmaleimide (5 mM), suggesting that the metals act on the SH-groups of enzyme. Moreover, the inhibitory effect of zinc (10-5 M) was significantly enhanced by S-100A (10-6 M) or calbindin (10-7 M), although neither protein had any effect in the presence of calcium (10-5 M) or copper (10-5 M). These results suggests that zinc has an unique role in the regulation of neutral phosphatase activity in rat brain cytosol.