O6-methylguanine DNA methyltransferase activity in liver from various fish species.

: O6-Methylguanine DNA methyltransferase (O6-MT) is considered to play an important role in the repair of alkylating carcinogen-induced lesions in a wide range of mammalian species. Fish are used widely in cancer research, one advantage being their high sensitivity to a variety of alkylating agents. To throw light on the mechanisms of DNA repair in the hitherto uninvestigated fish group, O6-MT activity was measured in liver from eight fish species belonging to six classes. Levels of O6-MT activity comparable with mouse values were found in liver of Japanese medaka (Oryzias latipes). Relatively low, but appreciable, levels of O6-MT activity were also observed in the other seven species examined. No adaptive increase in enzyme activity could be established in liver of rainbow trout following chronic dimethylnitrosamine pretreatment.