A rat monoclonal antibody which interacts with mammalian ornthine decarboxylase at an epitope involved in phosphorylation

Ornitine decarboxylase was purified from androgen-treated mouse kidney to homogeneity and high specific activity. The purified enzyme was utilized for production and screeing of rat monoclonal and polyclonal antibodies. A rat monoclonal antibody was isolated which was capable of immunoprecipitation of native mouse kidney ornitine decarboxylase activity or the [³H]difluoromethylornithine-inactivated enzyme. Phosphorylation of mouse ornithine decarboxylase by casein kinase-II prior to immunoprecipitation led to complete loss of the epitope recognized by the monoclonal antibody but did not alter recognition by polyclonal antibody. Mammalian ornithine decarboxylase activity obtainied from several species, in crude or partially purified extracts, was subjected to quantitative immunoprecipitatin with monoclonal and polyclonal antibody. Polyclonal antibody immunoprecipitated all of the ornthine decarboxylase activity from every extract tested, while monoclonal antibody was capable of only limited immunoprecipitation (60–80%). Due to the inability of the monoclonal antibody to recognize ornithine decarboxylase phosphorylated in vitrol by casein kinase-II and the partial immunoprecipitation of ornithine decarboxylase activity from cell extracts, a portion of the ornithine decarboxylase molecule population must exist in a phosphrylated state. This immunological evidence further confirms existing data that the enzyme in at least two distinct forms.