The objective of this research was to uncover possible regulatory differences in comparable inductions of ornithine decarboxylase (ODC) in two growth states. ODC activity increases 4-5 fold prior to DNA synthesis both in synchronous populations of continuously dividing cells and in quiescent cells stimulated to proliferate. The regulation of this particular enzyme activity in the two conditions is distinct in three ways. First, the addition of 2.0 mM hydroxyurea (HU) will block ODC induction in continuously dividing cells, while having no effect on ODC induction in stimulated quiescent cells. ODC induction in continuously dividing cells is remarkably sensitive to hydroxyurea, whose major effect is in limiting dATP pools. These data also indicate that ODC induction as a cell cycle event occurring previous to DNA synthesis, is not essential for transit of cells from G₁ into S phase. During a HU block, when ODC induction is prevented, cells arrest in early S phase. In addition, after HU is removed, 20% of the cellular DNA is synthesized before ODC activity ever increases. Experiments pursuing the mechanism whereby HU inhibits ODC induction showed that HU added after the induction has no effect on the enzyme activity. Administration of HU one hour previous to the induction prevents it. Therefore, HU is acting to prevent the process of ODC induction rather than simply effecting the enzyme activity. The decrease in ODC induction is not the consequence of a general cell cycle effect since another biochemical marker of the cell cycle (the activity and isozyme forms of adenosine 3', 5'-monophosphate dependent protein kinase) is not inhibited. In addition, general RNA and protein synthesis rates are not altered during an HU block. The inhibition of ODC is not due to a direct effect of HU on the enzyme, a diamine effect or an induction of the ODC antizyme. Hydroxyurea inhibits ribonucleoside diphosphate reductase (RdPR) and chelates ferrous ion. Experiments with a hydroxyurea analog, a less efficient inhibitor of RdPR, is less capable of inhibiting ODC activity. Addition of dithiothreitol resulting in an increased ferrous ion concentration, does not rescue ODC activity. Therefore, the induction of ODC in continuously dividing cells is presumably dependent upon deoxyribonucleoside triphosphates or their metabolites. The second distinct difference in ODC induction is that the expression of ODC in quiescent cells stimulated to proliferate is biphasic as these cells traverse G₁ and enter S phase. Only one peak of activity is apparent in synchronous cycling G₁ cells. The time interval between the first peak of ODC activity and the onset of DNA synthesis is approximately five hours longer in non-dividing cells stimulated to proliferate than in continuously dividing cells. This implies a different role of ODC in the two growth states. The third difference is that the induction of ODC in cells stimulated from quiescence toward DNA synthesis is sensitive to a microtubule inhibitor, colcemid. A microfilament inhibitor, cytochalasin B has less of an effect. In contrast, ODC induction in continuously cycling cells is not altered by colcemid. The biological half-life of ODC, when examined in both growth states was not different. The results presented here suggest that the regulation of an identical enzyme activity intimately connected with proliferative processes is different depending upon the growth state. The induction of ODC is continuously dividing cells occurs closer in time to DNA synthesis, is dependent upon deoxyribonucleoside triphosphate metabolism and independent of a microtubule inhibitor, colcemid. Further, although a temporal correlation between ODC induction and DNA synthesis exists, ODC is not essential for cellular progression into S phase but is required for the completion of DNA synthesis.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 168-181). Available also in a digital version from Dissertation Abstracts.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Includes bibliographical references.

No description available.

Thesis (doctoral)--Eberhard-Karls-Universität zu Tübingen, 1994.

Ornithine decarboxylase has been purified to apparent homogeneity from thioacetamide-stimulated calf liver. The purification process, which has been developed to circumvent the lability of the enzyme, employs ion exchange chromatography, gel filtration, hydroxylapatite chromatography, non-denaturing gel electrophoresis, and sulfhydryl affinity chromatography. The enzyme is purified 71,500-fold to a final specific activity of 286,000 pmol/min/mg protein. Non-denaturing gel electrophoresis indicates a single protein present in the final preparation. The enzyme has a Stokes radius of 3.14 nm as indicated by gel filtration and a monomeric molecular weight of 52,000 daltons as indicated by denaturing gel electrophoresis. The K(m) values for ornithine and pyridoxal phosphate are 0.16 mM and 2.5 μM, respectively. Putrescine inhibits the enzyme (Kᵢ 10mM). The existence of three ionic forms of ornithine decarboxylase is suggested by fractionation of the preparation by gradient sievorptive chromatography. Mammalian ornithine decarboxylase is apparently a metalloenzyme. A variety of structurally distinct metal chelators inhibit the enzyme. A non-chelating analog of the most potent chelator, 1,10-phenanthroline, is without effect. The order of efficacy of the chelators suggests the involvement of a metal from the transition series. Incubation of the enzyme with charcoal or Cibacron Blue-Agarose results in a loss of catalytic activity suggesting that the ornithine decarboxylase may also contain a bound nucleotide.

The aim of this study has been to elucidate the neural pathways involved in the regulation of adrenal ornithine decarboxylase (ODC) activity. Administration of the dopamine-receptor agonists apomorphine (APM) and piribedil (PBD) to rats led to an increase in ODC activity of both the adrenal medulla and cortex. These effects were blocked by giving the animals the dopaminergic antagonist haloperidol. The APM-induced increase in adrenomedullary ODC activity was largely prevented by denervation of the adrenal, transection of the spinal cord, and transection of the mesencephalon-diencephalon. Section of ventral spinal roots reduced the induction to varying extents, depending on the number of roots cut and their location between T(,4) and T(,12). The inducing effect of APM on adrenocortical ODC was abolished by hypophysectomy. Splanchnicotomy, rhizotomy and bilateral adrenal demedullation each attenuated the action of the drug. In contrast to this, section of the spinal cord or surgical isolation of the hypothalamus (preparation of "hypothalamic island") potentiated its effect. Impairment of serotonergic nerve function by systemic administration of p-chlorophenylalanine and intraventricular injection of 5,6'-dihydroxytryptamine or electrolytic potentiated the effect of APM in the adrenal medulla, but reduced it in the cortex. These observations suggest that adrenal ODC activity is predominantly regulated by one or more central facilitatory dopaminergic pathways. The pathway for the regulation of the medullary enzyme involves nuclei in the diencephalon-telencephalon and ultimately acts through the sympathetic nervous sytem. The pathway for the cortex involves the hypothalamus and acts via the anterior pituitary gland. These pathways include serotonergic components, which have opposite net effects on the induction of ODC produced by APM: inhibitory for the medulla and facilitatory for the cortex.

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Adelaide, Dept. of Animal Science, 1995? / Includes bibliographical references (leaves 255-280).