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PubMed2005

Benzoic acid transformation via conjugation with peptides and final fate of conjugates in higher plants.

Transformation of [1(14)C]- and [7(14)C] benzoic acids in sterile seedlings of maize (Zea mays) and pea (Pisum sativum) was studied. The tested labeled compounds were supplied in plants through roots as water solutions. The larger part of the assimilated benzoic acid forms conjugates with low-molecular-weight plant peptides. As a result of hydrolytic cleavage of the conjugation products, initial labeled benzoic acid molecules and unlabeled amino acids are released. It is supposed that conjugation takes place between the benzoic acid carboxyl group and the peptide functional groups. The amino acid composition of the conjugate peptides was determined. After removal of the plants from the labeled benzoic-acids-containing medium, the amount of conjugation products gradually decreases and the process is accompanied by the emission of labeled carbon dioxide, indicating that the conjugation products are degraded and that their radioactive component carbon atoms are then oxidized to carbon dioxide. Parallel to the conjugation reaction, a smaller part of the benzoic acid that entered the plant is transformed via oxidation, as a result of which an aromatic ring is cleaved and the resulting aliphatic fragment is incorporated into regular cell metabolism. The smallest part of the assimilated benzoic acid radiolabel is incorporated into a cell biopolymer fraction. Benzoic acid, of which the radioactive label is detected in the plant subcellular organelles and finally deposited in the vacuoles, affects the cell ultrastructural organization and the activities of the main metabolic enzymes. Intensification of catabolic processes takes place, indicating an energy demand needed for xenobiotic detoxification.

Amino Acids↗
PubMed1969

The fuel of respiration of rat kidney cortex.

1. In kidney-cortex slices from the well-fed rat, glucose (5mm) supplied 25-30% of the respiratory fuel; in the starved state, the corresponding value was 10%. These results are based on measurements of the net uptake of glucose and of the specific radioactivity of labelled carbon dioxide formed in the presence of [U-(14)C]-glucose. 2. Added acetoacetate (5mm) or butyrate (10mm) provided up to 80%, and added oleate (2mm) up to 50% of the fuel of respiration. The oxidation of endogenous substrates was suppressed correspondingly. 3. More [U-(14)C]oleate was removed by the tissue than could be oxidized by the amount of oxygen taken up; less than 25% of the oleate removed was converted into respiratory carbon dioxide and about two-thirds was incorporated into the tissue lipids. The rate of oleate incorporation into the neutral-lipid fraction was calculated to be equivalent to the rate of oxidation of endogenous fat, which provided the chief remaining fuel. 4. The contribution of endogenous substrates to the respiration (50%) in the presence of added oleate is taken to reflect either a high turnover rate of the endogenous neutral lipids (approx. half-life 2.5hr.) or a raised rate of lipolysis caused by the experimental conditions in vitro. 5. Added l-alpha-glycerophosphate (2.5mm) increased oleate incorporation into the neutral-lipid fraction by up to 40% (i.e. caused a net synthesis of triglyceride). 6. Lactate (2.5mm) added as sole substrate supplied 30% of the respiratory fuel, but with added oleate (2mm) lactate was converted quantitatively into glucose. Oleate stimulated the rate of gluconeogenesis from lactate by 45%. 7. The oxidation of both long-chain and short-chain even-numbered fatty acids was accompanied by ketone-body formation. Ketone-body synthesis from oleate, but not from butyrate, increased six- to seven-fold after 48hr. of starvation. The maximum rates of renal ketogenesis (80mumoles/hr./g. dry wt., with butyrate) were about 20% of the maximum rates observed in the liver (on a weight-for-weight basis) and accounted for, at most, 35% of the fatty acid removed. 8. dl-Carnitine (1.0mm) had no effect on the rates of uptake of acetate, butyrate or oleate or on the rate of radioactive carbon dioxide formation from [U-(14)C]oleate, but increased ketone-body formation from oleate by more than 100%. Ketone-body formation from butyrate was not increased. 9. There is evidence supporting the assumption that there are cells in which gluconeogenesis and ketogenesis occur together, characterized by equal labelling of [U-(14)C]oleate and the ketone bodies formed, and other cells that oxidize fat and do not form ketone bodies. 10. Inhibitory effects of unlabelled acetoacetate on the oxidation of [1-(14)C]butyrate and of unlabelled butyrate on [4-(14)C]acetoacetate oxidation show that fatty acids and ketone bodies compete as fuels on the basis of their relative concentrations. 11. The pathway of ketogenesis in renal cortex must differ from that of the liver, as beta-hydroxy-beta-methylglutaryl-CoA synthetase is virtually absent from the kidney. In contrast with the liver the kidney possesses 3-oxo acid CoA-transferase (EC 2.8.3.5), and the ready reversibility of this reaction and that of thiolase (EC 2.3.1.9) provide a mechanism for ketone-body formation from acetyl-CoA. This mechanism may apply to extrahepatic tissues generally, with the possible exception of the epithelium of the rumen and intestines.

Acetoacetates↗
PubMed1988

Measurement of specific radioactivity of tryptophan labeled with carbon-14 in plasma by high-performance liquid chromatography with a synchronized accumulating radioisotope detector.

Measurement of specific radioactivity by a high-performance liquid chromatograph with a synchronized accumulating radioisotope detector was conducted. Accuracy of measurement for an authentic sample containing 0.2 nCi of tryptophan labeled with carbon-14 exceeded 95%. In the case of a plasma sample obtained 120 min following intravenous administration of 15 muCi of labeled tryptophan to a rat, the coefficient of variation was 7.0%.

Animals↗
PubMed1989

Heme catabolism in cultured hepatocytes: evidence that heme oxygenase is the predominant pathway and that a proportion of synthesized heme is converted rapidly to biliverdin.

Heme oxygenase has been considered to be involved in the predominant pathway of heme degradation in vivo. However, alternative pathways involving cytochrome P-450 reductase, and lipid peroxidation, have previously been demonstrated in vitro, and studies with cultured rat hepatocytes were interpreted to show a majority of endogenous hepatic heme breakdown by non-heme oxygenase pathways. To clarify the pathway of heme breakdown in hepatocytes and the role of heme oxygenase in this process, cultured hepatocytes were pre-labelled with 5-[5-14C]aminolevulinate [( 14C]ALA). Radioactivity in heme, carbon monoxide, and bile pigments was measured for 8-24 h after the removal of [14C]ALA. In cultured chick embryo hepatocytes, which lack biliverdin reductase, the rate of production of biliverdin IXa was closely similar to the rate of catabolism of exogenous heme and radioactivity in carbon monoxide and biliverdin IXa was similar to the loss of radioactivity from endogenous heme. These results support the conclusion that heme breakdown occurred predominantly, if not solely, by heme oxygenase. Also, no evidence of non-heme oxygenase pathways was found in the presence of tin protoporphyrin, an inhibitor of heme oxygenase or mephenytoin, an inducer of both cytochrome P-450 and heme oxygenase. Similarly, in untreated cultured rat hepatocytes, radioactivity in carbon monoxide corresponded with loss of radioactivity in endogenous heme. In other experiments with chick hepatocyte cultures, rates of heme synthesis and breakdown were measured, and data were fitted to various models of hepatic heme metabolism. The results observed were consistent only with models in which an appreciable fraction (control cells, 17%, mephenytoin treated cells, 41%) of the newly synthesized heme was degraded rapidly to biliverdin.

Animals↗
PubMed2002

Reconstructing the history of 14C discharges from Sellafield: part 1--atmospheric discharges.

14C specific activities, above ambient background levels, were determined in individual treerings (corresponding to the years 1950-1999) sectioned from an oak tree that was felled in autumn 1999, from a location 1.5 km east of the Sellafield nuclear fuel reprocessing plant in Cumbria. north-west England. The data were used to produce a new, improved, reconstruction of Sellafield's annual atmospheric 14C discharges between 1951 and 1999, using the most reliable discharge data set (1994-1999) as the primary basis for the determination of a new calibration factor that relates excess 14C activity in individual tree rings to the annual discharge during the corresponding year. The results indicate that the current British Nuclear Fuels plc (BNFL) estimate of total 14C discharges to the atmosphere prior to 1978 is significantly overestimated, while the current estimate of total 14C discharges after 1978 is very similar to that determined in this study. In this study, the total activity of 14C discharged to the atmosphere from Sellafield between 1951 and 1999 is estimated to be 259+/-63 TBq (at 2 std. dev.). The BNFL current estimate is 360TBq.

Air Pollutants, Radioactive↗
PubMed1989

Assessment of radiological emissions from Spanish coal power plants: radioactive releases and associated risks.

The radioactivity of coals and ashes from Spanish coal power plants (CPP) was evaluated. This radioactivity is due mainly to 40K and the U and Th series. The samples were measured in secular equilibrium using a NaI(T1) detector. The annual average airborne releases were also evaluated. An atmospheric dispersion model was developed to predict the annual average concentration of radionuclides in air. The risks from inhalation were calculated and compared with those from nuclear power plants (NPP) and natural radioactivity.

Air Pollutants↗
PubMed1976

Biosynthesis of wound ethylene in morning-glory flower tissue.

Production of wound ethylene was investigated in rib segments excised from flower buds of morning-glory (Ipomoea tricolor). Segments of the ribs were cut from buds 2 days before flower opening, floated overnight on 5 mm KCl solution, and transferred to agar the following morning. These immature segments evolved only a small quantity of ethylene during incubation on agar, with most of the production occurring in the morning. When such segments were wounded mechanically early in the afternoon, the rate of ethylene production rose more than 10-fold within 1 hour and returned to a low rate after about 3 hours.Production of ethylene by both untreated and wounded rib segments was inhibited more than 95% by overnight pretreatment with the ethoxy analog of rhizobitoxine (3 x 10(-5) and 10(-4)m). After overnight exposure of segments to 9 muml-methionine-U-(14)C, the specific radioactivity of the ethylene evolved by untreated and wounded tissue was determined and compared to the specific radioactivities of carbon atoms 3 plus 4 of methionine and S-methylmethionine (SMM) extracted from the segments. The specific radioactivity of methionine was about one-half that of SMM; neither value was significantly affected by wounding. The specific radioactivity of ethylene evolved by untreated tissue was close to that of SMM. In wounded tissue the specific radioactivity of the ethylene evolved was lower, but still above that of methionine. These results are consistent with the interpretations that wound ethylene is synthesized from carbon atoms 3 plus 4 of either SMM or methionine. On the basis of earlier experiments with senescing rib segments, it is suggested that methionine serves as the precursor of the wound ethylene.

Journal Article↗
PubMed2002

Analysis and processing of samples for a carbon-14 monitoring program at a radioactive waste storage site.

A monitoring program was undertaken to determine the levels of airborne radioactive 14CO2 in an operating waste management area, and it its vicinity. As a part of this program, alkaline microporous pellets, recently developed, were used to sample the 14CO2 in air near waste storage structures and near the waste management area. These pellets were never fully characterized for their ability to capture high levels of 14CO2, and the processing and analysis needed to be improved to provide data on recoveries and consistencies, for an eventual method validation, with independent calibrations and standards. The sample analysis scheme also had to accommodate 14CO2 levels varying from near the natural background (250 Bq kg-1 C), to potentially three to four orders of magnitude above this value, near the wastes. The porous alkaline solid pellets were used for the passive capture of airborne 14CO2 over a period of weeks, to a few months. The pellets were processed to release the captured CO2 (14CO2 and 12CO2) into a NaOH solution, which was subsequently analyzed by liquid scintillation. Processing of the pellets yielded a 14C recovery of 96.0 +/- 4.2% and a lower, but consistent total carbon recovery, i.e., 85.9 +/- 2.7 and 86.9 +/- 2.6%, for procedural blanks and standards, respectively. The detection limits for the pellet sampling and processing was sufficient to reach environmental levels. For the higher levels of 14CO2 and for 'spot' sampling, we also used air samples, pumped into a NaOH solution to trap the 14CO2. These NaOH solutions were counted directly for 14C, also by liquid scintillation. The method limits of this latter technique, although much higher than for pellet samples, also achieved the performance objective for detecting airborne 14CO2. Both sampling and processing techniques, when used together, provided sufficient flexibility to be used for low (environmental) levels and high levels, near the wastes.

Air Pollutants, Radioactive↗