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Relationship between RNA polymerase I activity and ornithine decarboxylase in rat liver tissues.

ABSTRACT: In order to examine the relationship between RNA polymerase I and ornithine decarboxylase (ODC), three lines of experiments were performed, with the following results. The glucocorticoid-induced increase of RNA polymerase I in rat liver nuclei was not abolished by administration of inhibitors of ODC synthesis and activity, namely 1,3-diaminopropane and 2-difluoromethylornithine respectively. Anti-ODC antibody did not cross-react with RNA polymerase I solubilized from rat liver nucleoli, indicating the absence of a common protein sequence in these enzymes. The ODC preparation which was treated with transglutaminase in the presence of putrescine could not stimulate the activity of RNA polymerase I in nuclei of liver and prostate. All these results suggest that the increases in ODC protein or activity are not a prerequisite to the increase in RNA polymerase I after hormonal or physiological stimuli, but rather that the increases in both enzymes are separate responses to the primary stimuli.

SUBMITTER: Urata M

PROVIDER: S-EPMC1147539 | biostudies-other | 1987 Jan

REPOSITORIES: biostudies-other

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Project description:Repeated injections of 1,3-diaminopropane, a potent inhibitor of mammalian ornithine decarboxylase, induced protein-synthesis-dependent formation of macromolecular inhibitors or ;antienzymes' [Heller, Fong & Canellakis (1976) Proc. Natl. Acad. Sci. U.S.A.73, 1858-1862] to ornithine decarboxylase in normal rat liver. Addition of the macromolecular inhibitors, produced in response to repeated injections of diaminopropane, to active ornithine decarboxylase in vitro resulted in a profound loss of the enzyme activity, which, however, could be partly recovered after passage of the enzyme-inhibitor mixture through a Sephadex G-75 columin in the presence of 0.4m-NaCl. This treatment also resulted in the appearance of free inhibitor. In contrast with the separation of the enzyme and inhibitory activity after combination in vitro, it was not possible to re-activate, by using identical conditions of molecular sieving, any inhibited ornithine decarboxylase from cytosol fractions obtained from animals injected with diaminopropane. However, the idea that injection of various diamines, also in vivo, induces acute formation of macromolecular inhibitors, which reversibly combine with the enzyme, was supported by the finding that the ornithine decarboxylase activity remaining after diaminopropane injection appeared to be more stable to increased ionic strength than the enzyme activity obtained from somatotropin-treated rats. Incubation of the inhibitory cytosol fractions with antiserum to ornithine decarboxylase did not completely abolish the inhibitory action of either the cytosolic inhibitor or the antibody. A single injection of diaminopropane produced an extremely rapid decay of liver ornithine decarboxylase activity (half-life about 12min), which was comparable with, or swifter than, that induced by cycloheximide. However, although after cycloheximide treatment the amount of immunotitrable ornithine decarboxylase decreased only slightly more slowly than the enzyme activity, diaminopropane injection did not decrease the amount of the immunoreactive protein, but, on the contrary, invariably caused a marked increase in the apparent amount of antigen, after some lag period. The diamine-induced increase in the amount of the immunoreactive enzyme protein could be totally prevented by a simultaneous injection of cycloheximide. These results are in accord with the hypothesis that various diamines may result in rapid formation of macromolecular inhibitors to ornithine decarboxylase in vivo, which, after combination with the enzyme, abolish the catalytic activity but at the same time prevent the intracellular degradation of the enzyme protein.

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Relationship between RNA polymerase I activity and ornithine decarboxylase in rat liver tissues.

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