MANGANESE INHIBITS SUPEROXIDE-DISMUTASE ACTIVITY

Manganese is an essential trace element, which in excess causes neurot oxic Parkinsonian syndrome. Many toxic processes are mediated by oxyge n free radicals (OFR), and these are destroyed by several defense mech anisms including superoxide dismutase (SOD). SOD converts superoxide r adical to hydrogen peroxide. Manganese ion at a concentration of 0.83 mu g/ml, a little higher than that found in normal human brain tissue, inhibited SOD activity in an in vitro assay using 6-hydroxydopamine a s substrate. Mg had no effect at 0.33 mu g/ml, somewhat less than the normal brain manganese level. Mn had no effect on autoxidation of 6-hy droxydopamine in the absence of SOD in concentrations up to 1.67 mu g/ ml. It is concluded that Mn can inhibit SOD in vitro, and it is theref ore possible that in vivo manganese neurotoxicity may be mediated by e xcess OFR due to inhibition of intracellular cerebral SOD by manganese .