Purification and properties of ornithine decarboxylase from Tetrahymena pyriformis.

In Tetrahymena pyriformis, ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activities are present in the cytosolic and nuclear fractions and reach maximal values in the middle and late log phases of growth, respectively. The two activities have been purified to homogeneity by ammonium sulfate fractionation (20-45%), anion-exchange chromatography (DEAE-Bio-Gel A), gel-filtration (Sephadex G-150 and Sephadex G-100 superfine) and hydrophobic chromatography (Phenyl-Sepharose). Both the crude and the purified enzyme preparations are inactivated irreversibly by alpha-difluoromethylornithine, a suicide inhibitor of mammalian ornithine decarboxylase. The enzyme preparations from the nucleus and cytosol each showed a single band on polyacrylamide gel electrophoresis under native and denaturing conditions and on acrylamide gel electrofocusing. Both activities show the same pH optima (8.6) isoelectric point (5.3), molecular weight (64 000) and Kmorn (4.7 microM). The Km for L-lysine is 0.5 mM. The two activities also cross-react with acidic antizyme extracted from E. coli mutant MA 255. Based on the physicochemical properties, one can safely conclude that cytosolic and nuclear activities reside on the same protein molecule.