Effect of alpha-methyl ornithine on ornithine decarboxylase activity of rat hepatoma cells in culture.

DL-α-methyl ornithine (α-MeOrn), a potent competitive inhibitor of ornithine decarboxylase (L-ornithine carboxy-lyase EC 4.1.1.7) (ODC), caused an increase of ODC activity of rat hepatoma tissue culture cells cultured in the presence of the compound. The effect was seen only when there was newly synthesized ODC present. The α-MeOrn mediated increase of ODC activity was independent of RNA synthesis and was expressed at a post-transcriptional level. ODC half-life, measured after cycloheximide treatment, was increased by a factor of three in the presence of α-MeOrn, suggesting the compound slowed enzyme degradation perhaps by its ability to enter the active site.