Induction by chloroform of two forms of ornithine decarboxylase in rat liver

Pereira, Michael A.; Savage, Russell E.; Guion, Charles

doi:10.1016/0006-2952(83)90011-4

Cited by 21 publications

(1 citation statement)

References 14 publications

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“…A second group of studies demonstrated a difference in the intracellular halflife of the two major ionic forms of ODC eluted from anion exchange columns. In all the experimental systems used, including serum-stimulated HTC cells (55), livers from chloroform-treated rats (56) or kidneys from rats treated with dexamethasone, prolactin, or growth hormone (42), the second, more acidic form of ODC had a longer half-life than the first, more basic form. The increase in half-life of the more acidic ODC isoelectric form compared with the more basic form ranged from 2-to 100-fold in the various experimental systems studied.…”

Section: Induction Of Unphosphorylated and Phosphorylated Odc Inmentioning

confidence: 99%

Multisite Phosphorylation of Ornithine Decarboxylase in Transformed Macrophages Results in Increased Intracellular Enzyme Stability and Catalytic Efficiency

Reddy¹,

Mcllheran

Cochran

et al. 1996

Journal of Biological Chemistry

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Ornithine decarboxylase (ODC) is the initial inducible enzyme in the polyamine biosynthetic pathway. In the transformed macrophage-derived RAW264 cell line, ODC was overproduced and existed in both unphosphorylated and phosphorylated forms. To date, the only protein kinase known to phosphorylate mammalian ODC is casein kinase II (CKII). ODC was phosphorylated in vitro by CKII and subjected to exhaustive sequential proteolysis with trypsin and V8 protease. Two-dimensional peptide mapping showed only a single phosphopeptide; two-dimensional phosphoamino acid analysis of the phosphopeptide revealed only 32 P-labeled serine. ODC was metabolically radiolabeled with 32 P i in RAW264 cells and also subjected to proteolysis, two-dimensional peptide mapping, and phosphoamino acid analysis. Two phosphopeptides were generated from the metabolically radiolabeled ODC, including one that migrated similarly to the peptide phosphorylated by CKII in vitro. Each of the in situ radiolabeled ODC peptides contained both 32 P-labeled serine and threonine residues. Thus, in RAW264 cells, ODC is phosphorylated on at least one serine residue in addition to that phosphorylated by CKII and on at least two threonine residues. Phosphorylated ODC had an increased stability to intracellular proteolysis compared with unphosphorylated ODC, their half-lives being 49.2 ؎ 3.78 and 23.9 ؎ 2.6 min (p ‫؍‬ 0.001), respectively. The phosphorylated and unphosphorylated forms of ODC were independently purified to homogeneity. Kinetic analysis revealed that the catalytic efficiency of the phosphorylated form of ODC was 50% greater than that of the unphosphorylated form; the unphosphorylated ODC had a V max of 20.54 ؎ 1.65 mol/min/mg, whereas the phosphorylated form had a V max of 30.61 ؎ 2.6 mol/min/mg (p ‫؍‬ 0.005). Phosphorylation of ODC by CKII has no effect on enzyme activity. Taken together, these findings demonstrate that regulation of ODC activity is governed by as yet unidentified protein kinases.Ornithine decarboxylase (ODC, EC 4.1.1.17) 1 is the initial rate-limiting enzyme in polyamine biosynthesis. Putrescine, the product of ODC catalysis, and the subsequent metabolic pathway products spermidine and spermine are small aliphatic nitrogenous bases that fulfill structural and regulatory roles in protein and nucleic acid biosynthesis and function (1). Cellular ODC activity increases rapidly and transiently in response to trophic, proliferative, or toxic stimuli (2). Both somatic cell genetic and pharmacologic experimental approaches have demonstrated that expression of ODC is essential for cell growth. Regulation of enzyme expression at the levels of DNA transcription, mRNA translation, and protein turnover have been described (for reviews, see Refs. 3 and 4). However, little is known about potential posttranslational regulation of ODC.Multiple forms of ODC protein occur in a variety of cells and tissues. Anion exchange chromatography resolves several peaks of ODC activity in extracts prepared from calf liver (5), rat thymus and kidney (6), rat he...

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Section: Induction Of Unphosphorylated and Phosphorylated Odc Inmentioning

confidence: 99%

Multisite Phosphorylation of Ornithine Decarboxylase in Transformed Macrophages Results in Increased Intracellular Enzyme Stability and Catalytic Efficiency

Reddy¹,

Mcllheran

Cochran

et al. 1996

Journal of Biological Chemistry

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Ornithine decarboxylase properties: Is there a role for a microsome‐bound inactivating activity?

Zuretti

Brossa

Gili

et al. 1988

Cell Biochemistry & Function

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Liver microsomes have a strong ornithine decarboxylase (ODC) inactivating capacity in vitro. The present results suggest that this may be involved in regulation of ODC activity in vivo: (1) the O D C inactivating capacity of microsomes appears susceptible to in vivo modulation: a single administration of thioacetamide, which induces ODC, also causes a significant increase in the inactivating capacity of the microsomes; (2) under conditions leading to increased microsome-bound ODC-inactivating capacity (e.g. liver from thioacetamide-treated rates versus regenerating liver) ODC displays a greater thermal lability and inactivability in virro.A possible involvement of this microsomal activity in an autoregulatory pathway of O D C is suggested by the fact that it is induced by the administration of polyamines. However, inhibition of ODC activity by a-difluoromethylornithine does not prevent the increase of the microsomal activity caused by thioacetamide. Thus, polyamine biosynthesis does not appear to be an absolute requirement for induction of the microsomal ODC-inactivating capacity.The apparent half-life of O D C in vivo, as evaluated after cycloheximide administration, does not appear to correlate with the microsomal ODC-inactivating capacity content and the stability properties of O D C in vitro.

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