The antioxidant activity of metallothionein (MT) was investigated. Met
allothionein scavenged hydroxyl radicals (HO.)to protect DNA from the
oxidative attack by microsomes. This scavenging activity of MT was app
roximately 50 times greater than reduced glutathione (GSH) on a molar
basis. However, MT did not inhibit DNA damage induced by microsomes in
the presence of adriamycin (ADM)-Fe3+. Presumably, MT did not access
DNA at the binding site of ADM-Fe3+ by steric hindrance. The MT also i
nhibited microsomal lipid peroxidation induced by ADP-Fe3+ and NADPH.
The inhibitory activity of MT was about 10 times greater than GSH on a
molar basis. In addition, MT effectively inhibited the degradation of
R-phycoerythrin fluorescence induced by 2,2'-azobis-(2-amidino-propan
e)-dihydrochloride, suggesting that MT scavenges peroxyl radicals. Thi
s activity of MT was approximately 100 times greater than GSH on a mol
ar basis. Presumably, the inhibitory activity of MT against lipid pero
xidation is due to its ability to scavenge lipid peroxyl radicals on t
he membrane surface. The antioxidant activity of MT seems to be due to
MT scavenging free HO. and peroxyl radicals.