Intraperitoneal administration of 6.5 mg of methylated DNA, O6-methylguanine concentration being 11.5% that of guanine, to 3 month-old noninbred male rats was followed by a 5-fold decrease in the activity of O6-alkylguanine-DNA alkyltransferase (AT) within the first hour. The said enzyme is responsible for DNA O6-alkylguanine repair and plays a key role in mutagenic, carcinogenic and cytostatic effects of some alkylating agents. Within 24 hours, AT activity returned to normal to be followed by a significant increase. A correlation between the degree of inhibition of AT activity and dose of methylated DNA was established. Untreated DNA did not produce an inhibitory effect.
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