Purification and Properties of 3‐Methyladenine‐DNA Glycosylase from L‐Cells

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Abstract
3-Methyladenine-DNA glycosylase from mouse L-cells was purified approximately 800-fold. The enzyme is present primarily in the nucleus of the cells. The enzymatic reaction was sensitive to changes in the assay conditions and optimum activity was at pH 6.5 and at 100 mM KCl. Mg2+ did not effect the enzymatic reaction, which also worked in the presence of EDTA. The activity on denatured methylated DNA was 20-40% of that of the native double-stranded form. Sephadex gel filtration of the most purified fraction revealed enzyme species with MW of 68,000, 47,000 and 27,000, which differ from those reported for corresponding enzymes from other organisms. Addition of the product, 3-methyladenine, to the reaction mixture resulted in inhibition of the glycosylase activity of up to 60%. The remaining activity could not be abolished by increasing the concentration of 3-methyladenine.