Subcellular distribution of ornithine decarboxylase in rat liver and accessibility of the enzyme to alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase.

The subcellular localisation of ornithine decarboxylase and of its synthetic irreversible inhibitor, alpha-difluoromethylornithine, was investigated in control rat livers and in livers of animals in which the enzyme was induced by partial hepatectomy or by treatment with dexamethasone. Ornithine decarboxylase activity was distributed in normal rat liver between the nuclear (40%, mainly nucleolar) and the cytosolic (43%) fractions. Cytosolic liver ornithine decarboxylase was markedly induced after partial hepatectomy or treatment with dexamethasone, whereas the enzyme associated with the nuclear fraction was not induced by these procedures. The irreversible inhibitor was found only in the cytosol fraction and was totally absent from the nuclear fraction.