Protective effects of sodium selenite on killing and mutation by N-methyl-N'-nitro-N-nitrosoguanidine in E. coli.

Sodium selenite was found to protect Escherichia coli cells against killing and mutagenic effects of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). Such protective effects were not observed when cells were treated with N-methyl-N-nitrosourea (MNU). The protection by sodium selenite was not controlled by the ada gene, which is responsible for the repair of alkylated damage in DNA. A reduction of the amount of glutathione was found when cells were treated with sodium selenite, and glutathione is known to be involved in the methylation of DNA by MNNG, not by MNU. Reduced methylation by MNNG due to the reduction of the amount of glutathione caused by abundant sodium selenite was suggested to be the mechanism of protection.