Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.17 (ornithine decarboxylase)
 6,351 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Neurospora cells grown on minimal medium, most of the large ornithine pool is found in osmotically sensitive organelles, the "vesicles." In this paper kinetic studies on the compartmental behavior of ornithine and its derivatives are reported. Analysis of the metabolism of a 10(-7) M pulse of uniformly labeled L-[14C] ornithine supports the following conclusions: (a) Over 98% of the cellular ornithine is in the vesicles. (b) The amount of ornithine normally in the cytosol is about 0.3% of the cellular ornithine, as shown by the kinetics of incorporation of 14C into putrescine via the cytosolic enzyme, ornithine decarboxylase (EC 4.1.1.17). (c) Mitochondria, the site of ornithine synthesis, contain about 1% of the cellular ornithine, as demonstrated by the kinetics of incorporation of 14C into citrulline via the mitochondrial enzyme, ornithine transcarbamylase (EC 2.1.3.3). (d) Considerable ornithine exchange, and a net efflux of ornithine, takes place across the mitochondrial membrane. (e) Ornithine aminotransferase (EC 2.6.1.13), a catabolic enzyme, may have a special relation to the cell membrane in cells grown in minimal medium. This enzyme uses ornithine efficiently while it enters from the medium, but very poorly after all the [14C] ornithine is within the cell. (f) Citrulline and proline are not compartmented with respect to the enzymes using them. (g) In contrast, arginine is distributed such that over 99% is in vesicles. We suggest that the vesicles; with their ability to sequester ornithine and arginine, are potentially significant in regulation.
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PMID:Compartmental behavior of ornithine in Neurospora crassa. 13 43

Rats having a protein-free diet available ad libitum were fed a daily casein meal at the beginning of either the light- or the dark-phase of the day. A control group received a mixed-diet ad libitum. In all three groups, daily food ingestion was the same and casein corresponded to 12% of total intake. Liver activities of alanine, aspartate, ornithine and tyrosine aminotransferase, ornithine decarboxylase and serine dehydratase were assessed. In mixed-fed controls, all activities were low. Tyrosine aminotransferase and ornithine decarboxylase exhibited clear circadian rhythms of low amplitude. Feeding casein as a concentrated meal had no effect on aspartate aminotransferase. It depressed alanine aminotransferase and serine dehydratase activities. Tyrosine aminotransferase and ornithine decarboxylase exhibited rapid and strong stimulatory responses but, within 12 hours, returned to levels similar to those observed in mixed-fed controls. Ornithine aminotransferase was increased in the group receiving the casein meal during the light phase. It is concluded that the capacity for amino acid catabolism remains low in separately-fed animals, and that only tyrosine and especially ornithine, which may become limiting for urea synthesis, are actively metabolized. Thus, when high fluxes of amino acids reach the liver following the absorption of the casein meal, more amino acids are available for incorporation into newly synthesized proteins.
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PMID:Activity of several enzymes of amino acid catabolism in the liver of rats fed protein as a meal. 613 52

In the kidney, L-ornithine is reabsorbed along the proximal convoluted tubule (PCT), transported by basolateral carriers, and produced by arginase II (AII). Here, the renal metabolic fate of L-ornithine was analyzed in male and female rats. Kidneys and renal zones were dissected and used for Western blot analysis, immunofluorescence, and electron microscopic studies. Ornithine aminotransferase (OAT) and AII were localized using specific antibodies. Ornithine oxidation was determined by incubating microdissected tubules with L-[1-14C] or L-[U-14C]ornithine in the presence or absence of energy-providing substrates. Ornithine decarboxylase (ODC) mRNAs were localized by in situ hybridization. The 48-kDa OAT protein was detected in male and female kidneys, but its level was fourfold higher in the latter. OAT relative distribution increased from the superficial cortex toward the outer medulla to reach its highest level. Almost all OAT protein was localized in cortical and medullary proximal straight tubules (CPST and OSPST, respectively). In proximal straight tubule (PST), AII protein distribution overlapped that of OAT. No gender difference in AII protein level was found. OAT and AII were colocalized within PST mitochondria. L-[1-14C]ornithine decarboxylation occurred in all tubules, but predominantly in proximal tubules. L-[1-14C]ornithine decarboxylation was enhanced when L-[1-14C]ornithine was given to tubules as the sole substrate. The use of L-[U-14C]ornithine demonstrated the complete oxidation of ornithine. In conclusion, the OAT gene was expressed more in female rat proximal tubules than in male. Because OAT and AII proteins overlapped in PST mitochondria, L-arginine-derived ornithine may be preferentially converted to L-glutamate, as proven by ornithine oxidation. However, the coexpression of ODC, glutamate decarboxylase, and glutamine synthetase in PST suggests that L-ornithine can also be metabolized to putrescine, GABA, and L-glutamine. The fate of L-ornithine may depend on the cellular context.
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PMID:Ornithine metabolism in male and female rat kidney: mitochondrial expression of ornithine aminotransferase and arginase II. 1487 82

Ornithine aminotransferase (OAT) is a crucial enzyme in the synthesis of citrulline and arginine from glutamine/glutamate and proline by enterocytes of the small intestine. However, a role for OAT in intestinal polyamine synthesis and cell growth is not known. All-transretinoic acid (RA), an active metabolite of vitamin A, regulates the activity of several metabolic enzymes related to OAT, including ornithine decarboxylase and arginase, which may influence the function of OAT through effects on substrate (ornithine) availability. The objective of the present study was to test the hypothesis that RA regulates OAT mRNA expression and enzymatic activity in intestinal epithelial cells. Caco-2 cells were cultured for 12-72 h in the presence of 0, 0.01 and 1 microM RA and then used for measurements of OAT mRNA levels and enzyme activity as well as ornithine and polyamines. Treatment with RA induced increases in OAT gene expression and enzymatic activity, which resulted in decreased intracellular concentrations of ornithine and polyamines (putrescine, spermidine and spermine) in a dose-dependent manner. These changes occurred concomitantly with a decrease in the total number of cells, and the increase in OAT activity was due to increased OAT mRNA expression. In cells treated with 1 microM RA, addition of 10 microM putrescine to culture medium restored both cellular levels of polyamines and cell numbers to the values for the control group (without addition of RA). We conclude that exposure of Caco-2 cells to RA induces OAT expression for increasing ornithine catabolism. This leads to a reduced availability of intracellular ornithine for polyamine synthesis, thereby decreasing cell proliferation. These novel findings indicate a functional role for OAT in regulating intestinal polyamine synthesis and growth.
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PMID:Regulation of ornithine aminotransferase gene expression and activity by all-transretinoic acid in Caco-2 intestinal epithelial cells. 1828 Jan 34