A mutant of Chinese hamster ovary cells resistant to alpha-methyl- and alpha-difluoromethylornithine.

We describe a mutant of Chinese hamster ovary cells which is resistant to elevated levels of alpha-methylornithine and alpha-difluoromethylornithine, reversible and enzyme-activated irreversible inhibitors, respectively, of the enzyme ornithine decarboxylase (ODC). The mutant cells have significantly elevated levels of enzyme activity compared to wild-type cells, but several of the physical parameters of the enzyme are completely normal: Michaelis-Menten parameter, Km, affinity for the analog, and half-life. The temporal regulation of this activity in synchronized cells is not perturbed, and the suppression of ODC activity by the addition of putrescine is still observed. Indirect experiments suggest increased concentrations of ODC mRNA in the mutant cells.