Ornithine decarboxylase (ODC1) is an enzyme which belongs to the Orn/Lys/Arg decarboxylase class-II family. ODC1 is the rate-limiting enzyme of the polyamine biosynthesis pathway which catalyzes ornithine to putrescine. The activity level for the enzyme varies in response to growth-promoting stimuli and exhibits a high turnover rate in comparison to other mammalian proteins.