Ornithine decarboxylase. Purification and properties of ornithine decarboxylase

Gastric carcinogenesis in the rat induced by duodenogastric reflux without carcinogens: morphology, mucin histochemistry, polyamine metabolism, and labelling index

Chronic duodenogastric reflux induces gastric adenocarcinomas in the rat without the use of carcinogens. Altogether, 186 male Wistar rats were randomised to undergo either a simple gastrojejunostomy or a gastrotomy and sacrificed at eight weekly intervals for 56 weeks. No control animals developed dysplasia or carcinoma. All rats subjected to a gastrojejunostomy showed hyperplasia of the proliferative neck zone, with increased sulphomucin production adjacent to the scar. Low grade dysplasia was found at 16 weeks, and carcinoma was first seen at 32 weeks. Most carcinomas were well differentiated mucin secreting adenocarcinomas of the expanding type, which secreted a mixture of sialomucins and sulphomucins. Duodenogastric reflux was associated with a 100% increase in labelling index (assessed autoradiographically with tritiated thymidine) in the gastric mucosa when compared with corresponding tissue adjacent to a gastrotomy scar. This increase was significant at eight weeks and persisted for 56 weeks after surgery. This study supports the theory that, in this model, hyperplasia precedes the development of carcinoma.

Post-translational arginylation of ornithine decarboxylase from rat hepatocytes

Ornithine decarboxylase (ODC) was purified 6500-fold from NMRI mouse kidneys under conditions designed to inhibit degradation by proteinases. The enzyme was homogeneous by SDS/polyacrylamide-gel electrophoresis, and the specific activity was among the highest reported. The yield was 70%. A monoclonal antibody against this preparation was generated and used in studies to investigate the half-life of ODC in cultured rat hepatocytes labelled with [35S]methionine. This value was 39 +/- 4 min and was unchanged when either NH4Cl (as a lysosomotropic agent) or leupeptin (as a lysosomal proteinase inhibitor) was added to the culture medium. Thus the intracellular turnover of ODC in cultured hepatocytes occurs mainly in extra-lysosomal compartments. Arginylation of rat ODC was investigated in vitro by incubation with L-[3H]arginyl-tRNA, and the incorporation of the label was compared with that of total cytosolic proteins. Arginylated ODC had a specific radioactivity 8600 times that of the bulk of cytosolic protein. Edman degradation of this ODC showed that the post-translational arginylation occurred only at the alpha-amino end of the enzyme. The inhibitor of arginyl-tRNA:protein arginyltransferase (EC 2.3.2.8), L-glutamyl-L-valyl-L-phenylalanine, increased the half-life of ODC in cultured hepatocytes from 39 min to more than 90 min. The possible significance of the preferential post-translational arginylation of ornithine decarboxylase to its rapid turnover is discussed.

Multiple ionic forms of ornithine decarboxylase differ in degree of phosphorylation

Two major ionic forms of ornithine decarboxylase were separated by column chromatography of extracts of kidneys from androgen-treated male CD-1 mice on DEAE-Sepharose CL-6B, and purified individually to apparent homogeneity. On SDS-PAGE, a single major protein band of Mr 50000 was present in each. When incubated with casein kinase II, purified from rat liver cytosol, only one form of the enzyme, which represented 20% of the total ornithine decarboxylase in the tissue, became phosphorylated. The major form, which was eluted later from the column, could be phosphorylated only after treatment with alkaline phosphatase, indicating that the phosphatase removed enzyme-bound phosphate already attached at the casein kinase II phosphorylation site. Evidence for the occurrence of a phosphorylated form of the enzyme in kidneys of dexamethasone-treated rats is also presented.

Ornithine decarboxylase activity associated with a particulate fraction of brain

The enzymic decarboxylation of ornithine by adult rat brain largely occurs in the particulate fraction. The activity is primarily due to ornithine decarboxylase (ODC) as evidenced by several criteria: the concurrent production of equimolar amounts of CO2 and putrescine, the sensitivity of the reaction to difluoromethylornithine (DFMO), a specific inhibitor of ODC, the lack of major effect of two inhibitors of ornithine-2-oxo-acid transaminase, upon the DFMO-sensitive component of decarboxylation, the failure to profoundly reduce decarboxylation activity in the presence of a large excess of many aminoacids which could compete for non-specific decarboxylases. The insoluble ODC activity appears largely within synaptosomal and mitochondrial-enriched morphological fractions, yet cannot be attributed to trapped soluble ODC. Particulate ODC has a pH optimum and kinetic parameters that differ from those of soluble cerebral ODC.

Increased number of sympathetic neurons with unchanged target organ innervation after postnatal polyamine treatment

Treatment of newborn rats with polyamines from day 2 to day 9 after birth prevented the normal reduction in the number of sympathetic neurons in the superior cervical ganglion. About 40% more neurons prevailed in the ganglion after the polyamine treatment. This increase was paralleled by a comparable developmental increase in tyrosine hydroxylase activity and a small (17%) increase in choline acetyltransferase activity in the ganglion. However, in the iris, a target organ innervated by the sympathetic neurons, tyrosine hydroxylase activity and [3H]norepinephrine uptake remained unchanged. The results indicate that the polyamine-induced increase in the number of parent neurons is not accompanied by a change in the number of functional nerve terminals in the target organ.

c-rasH and ornithine decarboxylase are induced by oestradiol-17 beta in the mouse uterine luminal epithelium independently of the proliferative status of the cell

Oestradiol-17 beta (E2) treatment of the ovariectomized mouse results in a synchronised wave of cell proliferation in the uterine luminal epithelium. At the peak of DNA synthesis the mRNA level of the c-rasH proto-oncogene and ornithine decarboxylase were significantly increased. Progesterone treatment completely inhibits the E2 induced wave of DNA synthesis but does not greatly influence the level of these 2 mRNAs. Thus in the uterine luminal epithelium E2 regulates the level of ornithine decarboxylase and c-rasH independently of cell proliferation.

Polyamine treatment in early development leads to increased numbers of rat sympathetic neurons

Sympathetic and sensory neurons were counted in 35-day-old rats which were treated with polyamines from day 2 to day 9 after birth. The treatment led to an increase, averaging about 34%, in the number of sympathetic neurons in the superior cervical ganglion. The number of sensory neurons in the nodose ganglion was not changed. In sympathetic ganglia the activity of the neurotransmitter synthesizing enzyme tyrosine hydroxylase was also increased. The results demonstrate that increased polyamine supply during a limited developmental period can lead to an increased number of sympathetic neurons, possibly through enhanced neuron survival.

Inhibition of ornithine decarboxylase and glutamic acid decarboxylase activities by phosphorylethanolamine and phosphorylcholine

Ornithine decarboxylase, which catalyzes the first step in polyamine biosynthesis, is rapidly and transiently increased in various tissues during growth and after various hormonal or noxious stimuli, prior to an elevation in choline kinase activity. Polyamines themselves have been demonstrated to activate choline kinase. The present study sought to determine the effect of phosphorylcholine, the product of the reaction catalyzed by choline kinase, on ornithine decarboxylase activity. The data demonstrate that ornithine decarboxylase activity. The data demonstrate that ornithine decarboxylase activity is inhibited by phosphorylcholine and more potently by the related compound phosphorylethanolamine. The inhibition by both compounds led to decreased affinity of partially purified ornithine decarboxylase for ornithine. The inhibition is not time dependent and reversible. Both compounds also inhibit glutamic acid decarboxylase activity. The results suggest that high intracellular levels of phosphorylethanolamine and phosphorylcholine can serve as natural inhibitors of decarboxylases.