Effects of nickel on catalase activity in vitro and in vivo

The decomposition of H2O2 by catalase (CAT) was measured in a cell-free in vitro system in the presence of 0-24 mM Ni(II) or Mg(II) as well as in red blood cells (RBCs), and in post-mitochondrial fractions of liver and kidney of rats injected i.p. with 95 mumol/kg of nickel acetate. In vitro, immediately after addition of Ni(II), the inhibition of the catalytic activity of CAT (at 25 degrees C and pH 7.2) was directly proportional to Ni(II) concentration while Mg(II) had no effect. Following in vivo treatment, activity of CAT in the RBCs was decreased by 12% at 16 h, but had returned to control level by 48 h post injection. Hepatic CAT activity remained unchanged during the first 24 h after the injection but subsequently decreased by 25% at 48 h. Renal CAT first increased by 17% above the control levels at 16 h, returned to the control level at 24 h, and finally decreased by 27% at 48 h post injection. These changes neither concurred with the corresponding tissue concentrations of Ni(II) nor resembled the concentration/effect relationships observed in vitro. Thus, the mechanism by which Ni(II) inhibits CAT activity in vivo is more complex than that in vitro and cannot be solely related to direct Ni(II)-CAT interaction.