Effects of metallothionein on mutagenicity and oxidation of quercetin.

The effects of four types of Zn/Cd-metallothioneins on the mutagenicity of quercetin in Salmonella typhimurium TA98 were studied. The four types of Zn/Cd-metallothionein used in this experiment were metallothionein I, metallothionein I/II and metallothionein II from rabbit liver and metallothionein I/II from horse kidney. All four of the metallothioneins enhanced the mutagenicity of quercetin. Metallothionein II from rabbit liver, in which Zn content was the highest of the four metallothioneins, enhanced the mutagenicity of quercetin most effectively. Metallothioneins as well as Zn/Cu-SOD prevented quercetin oxidation under aerobic conditions. The action of these metallothioneins, which enhances the mutagenicity of quercetin, was fairly proportional to the activity which prevents quercetin from being oxidized. Reduced glutathione did not enhance the mutagenicity of quercetin although it did inhibit the quercetin oxidation. These results suggest that metallothioneins have superoxide (O2-) scavenging ability and act as "SOD-like" proteins in vivo. A simple and reliable system to detect biological substances which have antioxidant activity for the superoxide (O2-) was devised.