[The age-related dynamics of the activity of the DNA repair enzyme O6-alkylguanine-DNA alkyltransferase in different organs of rats].

Concentrations of O6-alkylguanine-DNA alkyltransferase (AT) which repairs a procarcinogenic DNA adduct O6-alkylguanine formed following exposure to carcinogenic N-nitroso compounds were measured in the liver, kidney and peripheral blood leukocytes of male L10 rats aged 1, 4, 14, 22 and 36 months. In the liver, peak AT level was observed at the age of 14 and 22 months. No age-related differences were established for kidney and leukocytes. The highest concentration of AT was registered in the kidney while the lowest--in leukocytes. The study revealed stoichiometric transfer of O6-methylguanine methyl group to cysteine residue of AT. No positive correlation was established between individual tissue AT levels in different animals. The highest level of total protein and the lowest concentration of DNA were observed in the liver and kidney of 14-22 month-old rats. The data obtained provide an explanation for relative resistance of 1-2 year-old rats to hepatotropic nitrosamine and suggest that the level of AT in a given tissue is not predictive of its activity in other tissues.