Abstract
Following partial hepatectomy, there is a dramatic enhancement in the residual liver in the activity of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17), an enzyme involved in polyamine synthesis. This increase in enzyme activity is completely prevented by treatment of the animals with puromycin at the time of hepatectomy, or by treatment with cycloheximide at the time of hepatectomy or up to 1 hr after hepatectomy. Actinomycin D administration at the time of operation prevents the subsequent rise in ornithine decarboxylase activity, but is only partially effective when given 30 min post-hepatectomy and ineffective 1 hr after operation. When cycloheximide is administered to unoperated rats or to animals 4 or 24 hr after hepatectomy, ornithine decarboxylase activity declines rapidly, with a half-life of about 11 min. After puromycin treatment, the decline of ornithine decarboxylase activity also shows a half-life of about 11 min. These findings suggest that the turnover of hepatic ornithine decarboxylase is extremely rapid.
ACKNOWLEDGMENTS The authors would like to thank Michael Kuhar and Dr. M. Walser for their assistance in describing kinetic considerations of turnover rates.
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