Ornithine decarboxylase turnover slowed by α hydrazino ornithine

α Hydrazino ornithine is a potent and selective inhibitor of ornithine decarboxylase (L ornithine carboxy lyase). When added to rat hepatoma cells at the time of dilution, α hydrazino ornithine elicits a dose related increase in ornithine decarboxylase activity and a concomitant prolongation of the apparent half life of the enzyme from 10 min to 28 min, as determined by the rate of decline of ornithine decarboxylase activity after inhibition of protein synthesis by cycloheximide. Similarly, systemic administration of α hydrazino ornithine to nephrectomized rats induces a dose related enhancement of ornithine decarboxylase activity in the normal and regenerating liver, which is associated with prolongation of the apparent half life of the enzyme. In both intact liver and hepatoma cells in culture, the decrease in the turnover rate of the enzyme can account for its increased activity.