Tissue-specific variation in repair activity for 3-methyladenine in DNA in two stocks of mice

Two stocks of mice, hybrid (C3H × 101)F₁ and inbred SEC/R1, were compared for 3-methyladenine-DNA N-glycosylase activity which is involved in removal of 3-methyladenine, 7-methylguanine and some other N-methylpurines in DNA, in cell-free extracts of different tissues. Based on activity measured both per unit weight of tissue and per mass DNA, there is a significant organ-specific and stock-specific difference in N-glycosylase activity over a range of 0.5-8.7 fmoles of 3-methyiadenine released per h at 37°C per fig DNA of tissue extract. On a per cell basis, the repair activity for 3-methyladenine is the highest in stomach in both stocks. The tissues can be arranged in order of decreasing activity of glycolytic removal as stomach > kidney > lung > liver > spleen > brain > ovary for SEC/R1 mice and stomach > kidney > ovary > spleen, lung and brain > liver for the hybrid mice. For all tissues except ovary, SEC/RI mice have 1.5-4-fold higher specific N-glycosylase activity than (C3H × 101)F₁ mice. In contrast, the ovary of SEC/R1 stock has about half as much enzyme activity as that of the hybrid stock.