The mechanism of action of 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (DIC) was studied by following the uptake of the drug by monolayer cultures of Chinese hamster cells. DIC was dramatically more inhibitory in the light than in the dark. Uptake of the ring moiety, as measured with DIC-2-14C, was also greater in the light than in the dark. The appearance of small amounts of 4-aminoimidazole-5-carboxamide and 2-azahypoxanthine in cells incubated in the dark suggests the activity of two pathways of DIC degradation. The greater uptake of DIC in the light may be attributable in part to efficient uptake of 2-azahypoxanthine by these cells.

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This work was supported by USPHS Grant CA 12429.

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