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DNA Methylase Inhibition In vitro by N-Methyl-N'-nitro-N-nitrosoguanidine¹

Cancer Research Laboratory, Veterans Administration Medical Center, Department of Biochemistry, University of Tennessee, Center for the Health Sciences, Memphis, Tennessee 38104

Several alkylating carcinogens were tested for their ability to inhibit DNA methylation in an in vitro assay. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) was the only carcinogen studied that altered the methylase activity. It was further demonstrated that MNNG reacts with the DNA methylase protein and produces a mixed type of inhibition. Prevention of the MNNG effect by dithiothreitol and inhibition of the DNA methylase with iodoacetamide suggest that DNA methylase is a sulfhydryl-containing enzyme and that MNNG inactivates the enzyme by reacting with sulfhydryl groups.

¹ This investigation was supported by the United States Veterans Administration (4323-01) and USPHS Research Grant CA-15189 from the National Cancer Institute.

Received 6/ 7/79. Accepted 10/10/79.