Spectrophotometric assay for ornithine decarboxylase

Radiosynthesis and evaluation of N5-(2-18F-fluoropropanyl) ornithine as a potential agent for tumor PET imaging

OBJECTIVE

Studies have confirmed that tumorigenesis is related to an imbalance of polyamine metabolism and over-expression of oncogenes resulting in the up-regulation of ornithine decarboxylase (ODC, the first rate-limiting enzyme for regulating intracellular polyamines biosynthesis), which has become a target for anti-tumor therapy. In this study, an ornithine derivative, N5-(2-[18F]fluoropropionyl) ornithine (N5-[18F]FPO), has been prepared and its potential utility for tumor PET imaging evaluated.

METHODS

N5-[18F]FPO was successfully prepared via a nucleophilic fluorination reaction and a subsequent efficient deprotection step. The in vitro and in vivo stability were determined by HPLC conducted in fetal bovine serum, saline and rat urine. Cellular uptake studies were conducted in HepG2 cells and the biodistribution and micro-PET/CT imaging performed in normal ICR mice and three tumor-bearing mice models, respectively.

RESULTS

Total synthesis time of N5-[18F]FPO was about 80 min with a radiochemical yield of 15% ± 6% (uncorrected, based on 18F-, n = 6) and a high radiochemical stability can be seen in vitro and vivo. The N5-[18F]FPO exhibited fast uptake in HepG2 cells and the cellular uptake ability of N5-[18F]FPO can be inhibited by L-ornithine and DFMO, which indicated that the transport pathway of N5-[18F]FPO is similar to that of L-ornithine, interacting with ODC after being transported into the cell. The biodistribution and micro-PET/CT images demonstrate that N5-[18F]FPO was excreted by the urinary system, and excellent tumor visualization with high tumor-to-background ratios can be observed in the three tumor-bearing mice models studied.

CONCLUSION

All the above results suggest that N5-[18F]FPO has the potential to be a novel radiotracer for imaging ODC expression in solid tumors.

DNA supercoiling differences in bacteria result from disparate DNA gyrase activation by polyamines

DNA supercoiling is essential for all living cells because it controls all processes involving DNA. In bacteria, global DNA supercoiling results from the opposing activities of topoisomerase I, which relaxes DNA, and DNA gyrase, which compacts DNA. These enzymes are widely conserved, sharing >91% amino acid identity between the closely related species Escherichia coli and Salmonella enterica serovar Typhimurium. Why, then, do E. coli and Salmonella exhibit different DNA supercoiling when experiencing the same conditions? We now report that this surprising difference reflects disparate activation of their DNA gyrases by the polyamine spermidine and its precursor putrescine. In vitro, Salmonella DNA gyrase activity was sensitive to changes in putrescine concentration within the physiological range, whereas activity of the E. coli enzyme was not. In vivo, putrescine activated the Salmonella DNA gyrase and spermidine the E. coli enzyme. High extracellular Mg2+ decreased DNA supercoiling exclusively in Salmonella by reducing the putrescine concentration. Our results establish the basis for the differences in global DNA supercoiling between E. coli and Salmonella, define a signal transduction pathway regulating DNA supercoiling, and identify potential targets for antibacterial agents.

Effect of Neuroterus quercusbaccarum (L.) galls on physiological and biochemical response of Quercus robur leaves

Gall formation is associated with multiple changes in plant cells, which still requires a better understanding. In this study, galls caused by sexual generation (♀♂) of Neuroterus quercusbaccarum (L.) (Hymenoptera: Cynipidae) on pedunculate oak trees (Quercus robur L.) were used as a model. Cytoplasmic membrane condition, concentration of hydrogen peroxide (H2O2), the activity of antioxidant enzymes and amino acid decarboxylase as well as chlorophyll fluorescence parameters were determined. Changes in physiological and biochemical parameters were analyzed in foliar tissues with galls and gall tissues themselves and compared to control. The presence of galls on oak leaves caused an increase of lipid peroxidation level. A significant decline in H2O2 and TBARS content with the reduction of guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity were observed in gall tissues. The activity amino acid decarboxylase, i.e., LDC, ODC and TyDC varied between samples, which may affect the content of amino acids. The presence of N. quercusbaccarum galls caused an insignificant increase of the chlorophylls, carotenoids and anthocyanin contents, while the content of pigments and their ratios in gall tissues was extremely low. Moreover, photosynthetic parameters (F0, Fm, Fv/Fm, Y, qP) were significantly decreased. Data generated in this study indicate that the development of N. quercusbaccarum galls on pedunculate oak leaves has a negative effect on host plant related to the disruption of cell membrane integrity, disturbance of photosynthesis and reduction of the antioxidant potential of the host plant.

Polyamines are required for normal growth in Sinorhizobium meliloti

Polyamines (PAs) are ubiquitous polycations derived from basic l-amino acids whose physiological roles are still being defined. Their biosynthesis and functions in nitrogen-fixing rhizobia such as Sinorhizobium meliloti have not been extensively investigated. Thin layer chromatographic and mass spectrometric analyses showed that S. meliloti Rm8530 produces the PAs, putrescine (Put), spermidine (Spd) and homospermidine (HSpd), in their free forms and norspermidine (NSpd) in a form bound to macromolecules. The S. meliloti genome encodes two putative ornithine decarboxylases (ODC) for Put synthesis. Activity assays with the purified enzymes showed that ODC2 (SMc02983) decarboxylates both ornithine and lysine. ODC1 (SMa0680) decarboxylates only ornithine. An odc1 mutant was similar to the wild-type in ODC activity, PA production and growth. In comparison to the wild-type, an odc2 mutant had 45 % as much ODC activity and its growth rates were reduced by 42, 14 and 44 % under non-stress, salt stress or acid stress conditions, respectively. The odc2 mutant produced only trace levels of Put, Spd and HSpd. Wild-type phenotypes were restored when the mutant was grown in cultures supplemented with 1 mM Put or Spd or when the odc2 gene was introduced in trans. odc2 gene expression was increased under acid stress and reduced under salt stress and with exogenous Put or Spd. An odc1 odc2 double mutant had phenotypes similar to the odc2 mutant. These results indicate that ODC2 is the major enzyme for Put synthesis in S. meliloti and that PAs are required for normal growth in vitro.

Inhibition of arginase via jugular infusion of Nω-hydroxy-nor-l-arginine inhibits casein synthesis in lactating dairy cows

A previous in vitro study revealed that Arg elicits positive effects on casein synthesis through alterations of the Arg-ornithine pathway in bovine mammary epithelial cells. The main purpose of this work was to determine the effects of arginase inhibition using N^ω-hydroxy-nor-l-arginine (nor-NOHA) on milk protein synthesis in vivo. Six healthy Chinese Holstein cows with similar body weight (550.0 ± 20 kg; means ± standard deviation), parity (4), body condition score (3.0), milk yield (21.0 ± 1.0 kg), and days in milk (80 ± 2) were selected and randomly assigned to 3 treatments in a replicated 3 × 3 Latin square design with 22 d for each period (7 d for infusion and 15 d for washout). The treatments were (1) control: saline infusion; (2) nor-NOHA: infusion of 125 mg/L of nor-NOHA; (3) nor-NOHA + Arg: infusion of 125 mg/L of nor-NOHA with 9.42 g/L of Arg. The activity of enzymes related to Arg metabolism, milk protein synthesis, and expression of AA transporters was determined. The infusion of nor-NOHA decreased the activity of arginase but had no effect on the activity of ornithine decarboxylase and nitric oxide synthase in serum, and these responses were the same at the gene expression level in mammary gland. In addition, the infusion of nor-NOHA also reduced protein and fat synthesis in milk but had no effect on milk yield. When Arg was infused with nor-NOHA, the activity of total arginase, ornithine decarboxylase, and nitric oxide synthase, and the concentration of casein, protein, and fat in milk did not change compared with the nor-NOHA group, but the milk protein yield, the expression of some Arg transporters (SLC7A5 and SLC7A8), and milk yield increased. Overall, results verified previous in vitro findings indicating that synthesis of casein protein is closely regulated by the Arg-ornithine pathway in bovine mammary gland.

The effect of Tetraneura ulmi L. galling process on the activity of amino acid decarboxylases and the content of biogenic amines in Siberian elm tissues

Tetraneura ulmi (L.), a member of Eriosomatinae subfamily, is one of the gall-forming aphids occurring on elms. Sap-sucking behaviour of founding mothers results in the formation of new plant organs. This study documents the changes in the content of plant biogenic amines (putrescine, cadaverine, spermidine, tryptamine, spermine and histamine) and key enzymes of their biosynthesis: lysine decarboxylase (LDC), tyrosine decarboxylase and ornithine decarboxylase (ODC) in galls and other parts of Siberian elm (Ulmus pumila L.) leaves during the galling process. The direction and intensity of these changes for particular amines and enzymes were dependent on the stage of gall development and part of the galling leaf. Generally, the amine content tended to increase in gall tissues during the 1st and 2nd period of the galling process and decreased in later phases. LDC and ODC activities were markedly enhanced, especially in gall tissues at the initial stage of the galling process.

Deep fried edible oils disturb hepatic redox equilibrium and heightens lipotoxicity and hepatosteatosis in male Wistar rats

Hepatosteatosis is a complex disorder, in which insulin resistance and associated dyslipidemic and inflammatory conditions are fundamental. Dietary habit, especially regular consumption of fat and sugar-rich diet, is an important risk factor. Coconut and mustard oils (CO and MO) are medium-chain saturated and monounsaturated fats that are common dietary ingredients among the Indian populations. Present study analyzed the effect of prolonged consumption of the fresh and thermally oxidized forms of these oils on glucose tolerance and hepatosteatosis in male Wistar rats. Thermally oxidized CO (TCO) and MO (TMO) possessed higher amount of lipid peroxidation products and elevated p-anisidine values than their fresh forms. Dietary administration of TCO and TMO along with fructose altered glucose tolerance and increased hyperglycemia in rats. Dyslipidemia was evident by elevated levels of triglycerides and reduced high density lipoprotein cholesterol (HDLc) levels in fructose and edible oil-fed group ( p < 0.05). Additionally, hepatic antioxidant status was diminished and oxidative stress markers were elevated in TCO- and TMO-fed rats. Substantiating these, hike in liver function marker enzyme activities were also observed in these animals. Supporting this, histological analysis revealed higher incidence of microvesicles and hepatocellular ballooning. Results thus suggest that consumption of thermally oxidized fats may cause hepatic damage.

Targeting Ornithine Decarboxylase by α-Difluoromethylornithine Inhibits Tumor Growth by Impairing Myeloid-Derived Suppressor Cells

α-Difluoromethylornithine (DFMO) is currently used in chemopreventive regimens primarily for its conventional direct anticarcinogenesic activity. However, little is known about the effect of ornithine decarboxylase (ODC) inhibition by DFMO on antitumor immune responses. We showed in this study that pharmacologic blockade of ODC by DFMO inhibited tumor growth in intact immunocompetent mice, but abrogated in the immunodeficient Rag1(-/-) mice, suggesting that antitumor effect of DFMO is dependent on the induction of adaptive antitumor T cell immune responses. Depletion of CD8(+) T cells impeded the tumor-inhibiting advantage of DFMO. Moreover, DFMO treatment enhanced antitumor CD8(+) T cell infiltration and IFN-γ production and augmented the efficacy of adoptive T cell therapy. Importantly, DFMO impaired Gr1(+)CD11b(+) myeloid-derived suppressor cells (MDSCs) suppressive activity through at least two mechanisms, including reducing arginase expression and activity and inhibiting the CD39/CD73-mediated pathway. MDSCs were one primary cellular target of DFMO as indicated by both adoptive transfer and MDSC-depletion analyses. Our findings establish a new role of ODC inhibition by DFMO as a viable and effective immunological adjunct in effective cancer treatment, thereby adding to the growing list of chemoimmunotherapeutic applications of these agents.

Discovery of novel inhibitors of human S-adenosylmethionine decarboxylase based on in silico high-throughput screening and a non-radioactive enzymatic assay

Natural polyamines are small polycationic molecules essential for cell growth and development, and elevated level of polyamines is positively correlated with various cancers. As a rate-limiting enzyme of the polyamine biosynthetic pathway, S-adenosylmethionine decarboxylase (AdoMetDC) has been an attractive drug target. In this report, we present the discovery of novel human AdoMetDC (hAdoMetDC) inhibitors by coupling computational and experimental tools. We constructed a reasonable computational structure model of hAdoMetDC that is compatible with general protocols for high-throughput drug screening, and used this model in in silico screening of hAdoMetDC inhibitors against a large compound library using a battery of computational tools. We also established and validated a simple, economic, and non-radioactive enzymatic assay, which can be adapted for experimental high-throughput screening of hAdoMetDC inhibitors. Finally, we obtained an hAdoMetDC inhibitor lead with a novel scaffold. This study provides both new tools and a new lead for the developing of novel hAdoMetDC inhibitors.

Molecular and functional profiling of the polyamine content in enteroinvasive E. coli : looking into the gap between commensal E. coli and harmful Shigella

Polyamines are small molecules associated with a wide variety of physiological functions. Bacterial pathogens have developed subtle strategies to exploit polyamines or manipulate polyamine-related processes to optimize fitness within the host. During the transition from its innocuous E. coli ancestor, Shigella, the aetiological agent of bacillary dysentery, has undergone drastic genomic rearrangements affecting the polyamine profile. A pathoadaptation process involving the speG gene and the cad operon has led to spermidine accumulation and loss of cadaverine. While a higher spermidine content promotes the survival of Shigella within infected macrophages, the lack of cadaverine boosts the pathogenic potential of the bacterium in host tissues. Enteroinvasive E. coli (EIEC) display the same pathogenicity process as Shigella, but have a higher infectious dose and a higher metabolic activity. Pathoadaption events affecting the cad locus have occurred also in EIEC, silencing cadaverine production. Since EIEC are commonly regarded as evolutionary intermediates between E. coli and Shigella, we investigated on their polyamine profile in order to better understand which changes have occurred along the path to pathogenicity. By functional and molecular analyses carried out in EIEC strains belonging to different serotypes, we show that speG has been silenced in one strain only, favouring resistance to oxidative stress conditions and survival within macrophages. At the same time, we observe that the content of spermidine and putrescine, a relevant intermediate in the synthesis of spermidine, is higher in all strains as compared to E. coli. This may represent an evolutionary response to the lack of cadaverine. Indeed, restoring cadaverine synthesis decreases the expression of the speC gene, whose product affects putrescine production. In the light of these results, we discuss the possible impact of pathoadaptation events on the evolutionary emergence of a polyamine profile favouring to the pathogenic lifestyle of Shigella and EIEC.

Effect of fluazifop-p-butyl treatment on pigments and polyamines level within tissues of non-target maize plants

Fluazifop-p-butyl (FL) is one of the most popular graminicides from arylophenoxypropionate group. These herbicides act as inhibitors of acetyl-CoA carboxylase (ACCase) that catalyzes the formation of malonyl-CoA during metabolism of lipids and/or of some secondary compounds. On the other hand arylopropionates and cyclohexanediones cause phytotoxic effects by stimulating free-radicals generation and causing oxidative stress in susceptible plants. However, the importance of disturbances in plant pigments and polyamines accumulation for this effect is not clear. The aim of this work is to quantify the phytotoxicity of FL to non target maize plant and to explain how photosynthetic pigments, anthocyanins (ANC) and polyamines participate in this interaction. Obtained results showed reduction of chlorophyll a and b, but only in case of the highest herbicide dose. Lower FL concentrations caused increase of the photosynthetic pigments, or were not effective. A similar effect was stated for putrescine, while spermidine was reduced within epicotyl of leaf tissues. In case of 2-phenylethylamine (PEA), there was observed a lack of significant changes within leaves and an increase in epicotyl under the middle and the highest dose of the herbicide. Moreover, FL induced ANC accumulation in epicotyls of maize seedlings. The activity of such key enzymes of polyamine biosynthesis as: ornithine decarboxylase (ODC) and lysine decarboxylase (LDC), increased in leaves treated with herbicide at the lowest concentration and decreased under the highest. However, in case of epicotyls the decreasing tendency was observed with the exception of ODC under the highest FL dose. The activity of tyrosine decarboxylase (TyDC) was importantly elevated only within epicotyls under the lower FL concentrations. It was concluded that FL inhibits maize growth, and the intensity of the effect is positively correlated with the herbicide concentration. The phenomenon was related to changes in content of pigments, polyamines and activity of studied enzymes.

Arginine-nitric oxide-polyamine metabolism in periodontal disease

BACKGROUND

Arginine is converted to nitric oxide (NO) via NO synthase and to ornithine via arginase. Ornithine decarboxylase (ODC) catalyzes the conversion of ornithine to polyamines. Arginase can inhibit NO production, and NO can inhibit ODC activity as part of an early inflammatory response. This study examines the arginine-NO-polyamine pathway alteration in saliva and gingival biopsy samples of patients with gingivitis or periodontitis and healthy controls and evaluates the response to periodontal treatment.

METHODS

This study includes nine gingivitis patients, 15 chronic periodontitis patients, and 11 healthy age-matched controls. Periodontal clinical measurements, gingival biopsies, and saliva samples were obtained before treatment (BT) and 1 month after periodontal treatment (AT). Arginase and ODC activities and NO levels were determined spectrophotometrically.

RESULTS

The BT salivary and gingival NO levels were found to be highest in the gingivitis group, followed by the healthy and the periodontitis groups, respectively. Salivary NO levels significantly increased in the periodontitis group and decreased in the gingivitis group AT (P <0.05). Gingival NO levels decreased significantly in the periodontitis and the gingivitis groups AT (P <0.05). Arginase levels were detected highest in the gingivitis group and lowest in the periodontitis group, both in saliva and gingiva. Only gingival arginase levels significantly increased AT (P <0.05). ODC activity was highest in saliva, and lowest in the gingiva of the periodontitis patients BT. It was found to be significantly higher in the periodontitis group AT (P <0.05).

CONCLUSIONS

In this study, regarding arginine-NO-polyamine metabolism, gingival tissue seems to be more informative about periodontal pathogenesis than saliva. At early phase of periodontal inflammation, NO arginase and ODC levels were measured as higher than at an established lesion of periodontitis.

L-arginine reduces cell proliferation and ornithine decarboxylase activity in patients with colorectal adenoma and adenocarcinoma

PURPOSE

Evidence suggests that the majority of colorectal carcinomas arise from adenomas, and L-arginine suppresses colorectal tumorigenesis. We suppose that L-arginine may inhibit the process of carcinogenesis from colorectal adenoma to adenocarcinoma. The aim of this study was to investigate the effects of L-arginine on the formation and development of colorectal tumors.

EXPERIMENTAL DESIGN

We selected 60 patients with colorectal cancer and 60 patients with colorectal adenoma (CRA) and divided them into four groups of 30 patients each. We gave 30 g (120 mL) of L-arginine everyday for 3 days to the test groups, whereas L-arginine was substituted by 5% glucose in the control groups. The expression of the proliferating cell nuclear antigen, survivin, and nitric oxide synthase was examined immunohistochemically, and ornithine decarboxylase (ODC) activity was examined spectrophotometrically. Serum nitric oxide (NO) was detected by the Griess assay.

RESULTS

In patients with CRA, the proliferating cell nuclear antigen and survivin labeling indexes and ODC activity of the tumor and paratumor mucosa in the L-arginine-treated group after L-arginine treatment were significantly lower as compared with the corresponding pretreatment values (P < 0.01). Moreover, inducible nitric oxide synthase expression in the tumor markedly increased after L-arginine treatment (P < 0.05). Serum NO levels in the patients with colorectal cancer were markedly higher than those in the patients with CRA, and L-arginine treatment was responsible for this increase (P < 0.05).

CONCLUSIONS

Our results show that L-arginine can restrain crypt cell hyperproliferation and the expression of survivin, an inhibitor of apoptosis protein. This suggests that L-arginine can block the formation and development of colorectal tumors, and this effect might be related to the increased serum NO concentration and decreased ODC activity.

Regulatory effects of corticosterone on ornithine decarboxylase activity during liver regeneration in rats

AIMS

The regulation of ornithine decarboxylase (ODC) gene expression and enzyme activity by corticosterone during rat liver regeneration induced by partial hepatectomy (PH) was evaluated.

METHODS

Bilateral adrenalectomies were performed on ether-anesthetized rats 3 days before PH. Corticosterone in sesame oil was injected subcutaneously to adrenalectomized rats. ODC mRNA, ODC protein and enzyme activity were detected by in situ hybridization, Western blot and high performance liquid chromatography (HPLC), respectively.

RESULTS

The ODC mRNA levels, protein accumulation and enzyme activity were lower in the intact liver compared to the regenerating liver. After PH, mRNA levels were remarkably enhanced in all groups and peaked at 5 h post-PH, and presented a persistent increase only in adrenalectomy rats during the regeneration process. Corticosterone treatment resulted in a dose-dependent decrease in ODC mRNA content after 5 h post-PH. ODC protein accumulation in adrenalectomy rats was higher than that in sham-adrenalectomy rats, but it decreased in corticosterone-treated (10 mg/kg) rats until 24 h post-PH, with a strong decline seen in 40 mg/kg corticosterone-treated rats. ODC activity was rapidly promoted, and the highest levels were observed at 6 h after PH in all groups. After corticosterone treatment, the activities declined significantly at 6 h post-PH, with the lowest value found in the 40 mg/kg group.

CONCLUSIONS

Corticosterone treatment results in dose-dependent decreases in ODC mRNA and enzyme protein both in the intact liver and the regenerating liver. The change in ODC activity is partially related to alterations of ODC mRNA and protein accumulation.

Conjugated linoleic acids exhibit a strong fat-to-lean partitioning effect, reduce serum VLDL lipids and redistribute tissue lipids in food-restricted rats

Effects of conjugated linoleic acids (CLA) on a series of metabolic events are expected to depend on the feeding regimen and levels of energy ingested. This study was the first examining the mode of action of CLA on body composition, tissue lipids, lipoproteins and hepatic enzymes in situations of enhanced fat store mobilization. Two groups of male growing Sprague-Dawley rats were fed for 3 wk a diet containing 0 (control group) or 3 g/100 g of a CLA mixture at the expense of sunflower oil, and were then subjected to a weight-loss feeding regimen for another 18 d. Rats fed the CLA-fortified diet gained 11% less weight than the control rats (P<0.05). Rats fed the high CLA diet had less body fat (1.47+/-0.16 vs. 1.07+/-0.09 g/100g, P<0.05) and a higher lean deposition (25.6+/-0.2 vs. 28.4+/-0.3 g/100 g, P<0.05) than control rats. CLA-fed rats had a 41% lower cholesterol concentration in liver than the control rats (P<0.05). Some differences in glycerophospholipid subclass profile of liver and erythrocyte membrane were observed; the hepatic concentrations of phosphatidylethanolamine (4.76+/-0.46 vs. 6.86+/-0.99 micromol/g, P = 0.07) and phosphatidylcholine (12.9+/-0.5 vs. 15.3+/-1.2 micromol/g, P = 0.09) tended to be greater and the level of phosphatidylcholine in erythrocyte membranes was significantly greater (1.40+/-0.12 vs. 1.83 +/-0.16 micromol/g, P<0.05) in the CLA-treated group than in the control group. The activities of catalase and ornithine decarboxylase in liver did not differ between the groups. Further, CLA-treated rats had significantly lower serum concentrations of VLDL lipids than control rats, whereas concentrations of LDL and HDL lipids were unaffected. The results indicate that a high dose of a CLA mixture is a strong repartitioning agent and a modulator of lipid metabolism under conditions of enhanced fat store mobilization in rats.

Ornithine decarboxylase activity and its gene expression are increased in benign hyperplastic prostate

BACKGROUND

Ornithine decarboxylase (ODC) is the first key enzyme in the polyamine biosynthesis pathway. Polyamine is believed to participate in cellular proliferation and differentiation. To study the relationship between ODC and the pathogenesis of benign prostatic hyperplasia (BPH), the polyamine levels, ODC activities, and expression of ODC mRNA in benign hyperplastic and normal human prostates were assayed.

METHODS

Polyamine contents and ODC activities in tissue extracts were determined by reverse-phase high-performance liquid chromatography and spectrophotometric procedures, respectively. The ODC mRNA levels were assayed by Northern blot analysis.

RESULTS

The contents of putrescine, spermidine, and spermine in BPH tissues were 2.2, 3.4, and 6.0 times higher than those in normal tissues, respectively; the ODC activity of BPH tissue was about 3.2 times higher than in normal tissue; the expression level of ODC mRNA in the BPH tissues was greater than that of normal tissues.

CONCLUSIONS

The findings imply that 1) the increased ODC activity and polyamine content in prostatic tissue may correlate with the pathogenesis of BPH, and 2) the high level of ODC activity is induced by the overexpression of ODC mRNA.

The effect of different doses of epidermal growth factor on liver ornithine decarboxylase and Na-K ATPase activities in newborn rats

1. Ornithine decarboxylase and Na-K ATPase activities were studied in rat livers that were treated with different doses of epidermal growth factor (EGF). 2. The ornithine decarboxylase activities were studied with spectrophotometry, and results were expressed as micromoles of putrescine per hour per milligram of protein. Na-K ATPase activities were studied on the basis of the principle of measuring the amount of inorganic phosphates released by the hydrolysis of ATP, and the results were expressed as micromoles of inorganic phosphate per hour per milligram of protein. 3. When compared with the controls, although the Na-K ATPase activities were decreased at low doses of EGF, their activities were found to be increased at high doses of EGF. On the other hand, there was a positive correlation between ornithine decarboxylase activities and EGF doses. 4. The results of this study suggest that, whereas the decrease in Na-K ATPase activities at low doses of EGF can be due to the utilization of the enzyme, the increase in Na-K ATPase activities at high doses of EGF can be attributed to its enhanced synthesis.

Pyridoxal 5'-phosphate dependent enzymes in the nematode Nippostrongylus brasiliensis

Eight classes of pyridoxal 5'-phosphate dependent enzymes have been investigated in Nippostrongylus brasiliensis in parallel with rat tissues. The range of decarboxylases detected in N. brasiliensis was limited in comparison with rat tissues. N. brasiliensis possessed a highly active L-serine hydroxymethyltransferase, but in contrast with rat liver, 5-aminolevulinic acid synthetase was absent. Similar levels of L-serine and L-threonine dehydratase activities were detected in N. brasiliensis and rat liver, and both organisms lacked L-alanine racemase, L-tryptophan synthetase and L-methionine gamma-lyase. The demonstration of cystathionine beta-synthase and gamma-cystathionase in N. brasiliensis suggests the presence of a functional trans-sulphuration sequence. The substrate specificities of the nematode cystathionine beta-synthase and gamma-cystathionase varied significantly from those of the corresponding mammalian enzymes. Particularly striking was the ability of N. brasiliensis cystathionine beta-synthase to catalyse the non-mammalian 'activated L-serine sulphydrase' reaction (L-cysteine + R-SH----cysteine thioether + H2S). N. brasiliensis and rat liver exhibited comparable abilities to transaminate amino acids via the 2-oxoglutarate: glutamate system.

Expression of a bacterial lysine decarboxylase gene and transport of the protein into chloroplasts of transgenic tobacco

A possible approach for altering alkaloid biosynthesis in plants is the expression of genes encoding key enzymes of a pathway such as lysine decarboxylase (ldc) in transgenic plants. Two strategies were followed here: one focused on expression of the gene in the cytoplasm, the other on subsequent targeting of the protein to the chloroplasts. The ldcgene from Hafnia alvei was therefore (a) placed under the control of the 1' promoter of the bidirectional Tr promoter from Agrobacterium tumefaciens Ti-plasmid, and (b) cloned behind the rbcS promoter from potato fused to the coding region of the rbcS transit peptide. Both ldc constructs, introduced into Nicotiana tabacum with the aid of A. tumefaciens, were integrated into the plant genome and transcribed as shown by Southern and northern hybridization. However, LDC activity was only detectable in plants expressing mRNA under the control of the rbcS promoter directing the LDC fusion protein into chloroplasts with the aid of the transit peptide domain. In plants expressing the processed bacterial enzyme cadaverine levels increased from nearly zero to 0.3-1% of dry mass.

Enzymes used in predicting high risk to colon cancer

Attempts have been made to use enzyme assays primarily in tissue, to predict risk of colon cancer in high risk colon cancer families, and in patients with polyposis. Efforts have also been made to predict recurrence in surgically "cured" cancer patients. The use of thymidine kinase, ornithine decarboxylase, LDH isoenzymes, and other enzymes for these purposes will be reviewed.

Ornithine decarboxylase in resting human mononuclear leucocytes: evidence for an endogenous inhibitor

1. Ornithine decarboxylase (ODC) was measured in human mononuclear leucocytes (HML) by retention of putrescine on cation exchange paper. 2. The method was validated with unstimulated HML, phytohemagglutinin-stimulated HML, and a commercial preparation of ODC. The average enzyme activity of unstimulated HML (50 samples) was 22.6 +/- 7.3 pmol/hr 10(7) cells, with 29 values less than 5 pmol/hr 107 cells. 3. The results show that an endogenous inhibitor or inactivator of ODC exists in unstimulated HML: enzyme activity in extracts of mitogen-stimulated cells were inhibited by extracts of unstimulated cells (37-55%) inhibition under the conditions used.