Antioxidant activity of metallothionein compared with reduced glutathione.

The antioxidant activity of metallothionein (MT) was investigated. Metallothionein scavenged hydroxyl radicals (HO.) to protect DNA from the oxidative attack by microsomes. This scavenging activity of MT was approximately 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 inhibited 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-propane)-dihydrochloride, suggesting that MT scavenges peroxyl radicals. This activity of MT was approximately 100 times greater than GSH on a molar basis. Presumably, the inhibitory activity of MT against lipid peroxidation is due to its ability to scavenge lipid peroxyl radicals on the membrane surface. The antioxidant activity of MT seems to be due to MT scavenging free HO. and peroxyl radicals.