Lead (Pb) inhibited the activities of Na+ -K+ ATPase (IC50= 2.0×10^(-6) M), K + -Para-Nitrophenyl phosphatase (PNPPase) (IC50= 3.5×10^(-6) M) and [3H]-ouabain binding (IC50 = 4.0×10^(-5) M) in rat brain...Lead (Pb) inhibited the activities of Na+ -K+ ATPase (IC50= 2.0×10^(-6) M), K + -Para-Nitrophenyl phosphatase (PNPPase) (IC50= 3.5×10^(-6) M) and [3H]-ouabain binding (IC50 = 4.0×10^(-5) M) in rat brain P2 fraction. A variable temperature or pH significantly elevated the inhibition of Na+-K+ ATPase by Pb in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation of Na+ -K+ ATPase by ATP was indicated by a variation in Vmax values with no significant changes in Km values at any temperature studied. In the presence of Pb, for Na+ -K+ ATPase at pH 6.5 and 8.5, Vmax was decreased with an increase in Km values suggesting a mixed type of inhibition. Sulfhydryl agents such as dithiothreitol (DTT) and cvsteine (Cyst), but not glutathione (GSH) offered varied levels of protection against Pb-inhibition of Na + -K+ ATPase at pH 7.5 and 8.5. The present data suggest that inhibition of Na+ -K+ ATPase by Pb is both temperature and pH-dependent. These results also indicate that Pb inhibited Na + -K + ATPase by interfering with phosphorylation of enzyme molecule and dephosphorylation of the enzyme-phosphoryl complex and exerted an effect similar to that of SH-blocking agents.展开更多
文摘Lead (Pb) inhibited the activities of Na+ -K+ ATPase (IC50= 2.0×10^(-6) M), K + -Para-Nitrophenyl phosphatase (PNPPase) (IC50= 3.5×10^(-6) M) and [3H]-ouabain binding (IC50 = 4.0×10^(-5) M) in rat brain P2 fraction. A variable temperature or pH significantly elevated the inhibition of Na+-K+ ATPase by Pb in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation of Na+ -K+ ATPase by ATP was indicated by a variation in Vmax values with no significant changes in Km values at any temperature studied. In the presence of Pb, for Na+ -K+ ATPase at pH 6.5 and 8.5, Vmax was decreased with an increase in Km values suggesting a mixed type of inhibition. Sulfhydryl agents such as dithiothreitol (DTT) and cvsteine (Cyst), but not glutathione (GSH) offered varied levels of protection against Pb-inhibition of Na + -K+ ATPase at pH 7.5 and 8.5. The present data suggest that inhibition of Na+ -K+ ATPase by Pb is both temperature and pH-dependent. These results also indicate that Pb inhibited Na + -K + ATPase by interfering with phosphorylation of enzyme molecule and dephosphorylation of the enzyme-phosphoryl complex and exerted an effect similar to that of SH-blocking agents.
