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PubMed1969

Control of the citric acid cycle by glyoxylate. The mechanism of inhibition of oxoglutarate dehydrogenase, isocitrate dehydrogenase and aconitate hydratase.

1. The effects of glyoxylate on partially purified preparations of aconitate hydratase, isocitrate dehydrogenase and oxoglutarate dehydrogenase were compared with those of oxalomalate and hydroxyoxoglutarate (obtained by condensation of glyoxylate with oxaloacetate and pyruvate respectively). 2. Glyoxylate (1mm) did not affect aconitate hydratase and isocitrate dehydrogenase, whereas oxalomalate (1mm) inhibited the enzyme activities completely. 3. Glyoxylate (0.025mm) inhibited oxoglutarate dehydrogenase irreversibly, whereas the same concentrations of oxalomalate and hydroxyoxoglutarate were ineffective. This inhibitory effect was prevented if oxoglutarate, pyruvate or oxaloacetate was mixed with the enzyme before the glyoxylate. 4. Incubation of oxoglutarate dehydrogenase with radioactive glyoxylate produced radioactive carbon dioxide; radioactivity was also recovered in the portion of the enzyme identified with thiamin pyrophosphate. 5. The behaviour of glyoxylate in producing multiple inhibitions of the citric acid cycle, either by direct interaction with oxoglutarate dehydrogenase, or by means of its condensation compounds which inhibit aconitate hydratase and isocitrate dehydrogenase, is discussed.

Animals↗
PubMed1978

Scintigraphic detection of pulmonary emboli by serial positron imaging of inhaled 15O-labeled carbon dioxide.

Inhaled radioactive carbon dioxide is retained in pulmonary blood distal to embolic obstruction and appears as an area of increased radioactivity that delineates the site and magnitude of the affected zone. The scintigraphic detection of pulmonary emboli by serial imaging of inhaled carbon dioxide labeled with cyclotron-produced 15O2 was evaluated in 27 patients undergoing conventional pulmonary ventilation/perfusion imaging and pulmonary arteriography. Fifteen patients proved to have pulmonary emboli on arteriography. Sensitivity (87%) and specificity (92%) rates for inhalation imaging were superior to those of conventional ventilation/perfusion imaging (P less than 0.05). Clearance of 15O2 activity was markedly delayed over embolized pulmonary segments (mean half time of 47.0 +/- 11.1 seconds [S.E.M.]) in comparison to normal segments (mean of 3.6 +/- 0.08 seconds; P less than 0.001). Pulmonary imaging by this method provides an approach to the detection of pulmonary emboli that is relatively sensitive and specific and permits analysis of persisting perfusion in embolized pulmonary segments. A major practical limitation, however, is the necessity of a nearby cyclotron.

Adult↗
PubMed1983

Precursor of carbon atom five and hydroxymethyl carbon atom of the pyrimidine moiety of thiamin in Escherichia coli.

The pyrimidine moiety of thiamin can be synthesized in bacteria from 5-aminoimidazole ribotide (AIR), an intermediate in purine biosynthesis. To transform the imidazole ring of AIR to the pyrimidine, the bond between C-4 and C-5 of the imidazole ring should be ruptured and a two-carbon unit should be inserted. We investigated a precursor of the two-carbon unit which should be inserted to form the pyrimidine. To examine the possibility of the two-carbon compound as a precursor which is formed from a three-carbon intermediate in the glycolytic pathway and its three-carbon derivative by decarboxylation in cells, we studied the incorporation of [2-14C]glycerol, [2-14C]pyruvate, [U-14C]alanine and [3-14C]serine into the pyrimidine by Escherichia coli. Glycerol, pyruvate and alanine were not incorporated into the pyrimidine. Radioactive carbon of [3-14C]serine was incorporated into C-2 of the pyrimidine via one-carbon units pool. Then, we investigated the possibility of a ribose moiety of AIR being a precursor of the two-carbon unit. As ribose has low permeability into E. coli cells, the ribose moiety of AIR was labeled with [14C]glucose which was added to the growth medium. The results show that two radioactive carbons of [U-14C]glucose were incorporated into the pyrimidine and radioactive carbon of [6-14C]glucose was incorporated into hydroxymethyl carbon attached to C-5 of the pyrimidine. The dilution rates of the specific radioactivity of the pyrimidine from [U-14C]glucose and [6-14C]glucose well coincide with those of the ribose moiety of the nucleotide (AMP). Radioactive carbon of [1-14C]glucose was not incorporated into the pyrimidine and nucleotide. It is concluded that the two-carbon fragment derived from C-4' and C-5' of the ribose moiety of AIR can be incorporated into the pyrimidine moiety of thiamin as the precursor of C-5 and hydroxymethyl carbon.

Alanine↗
PubMed1999

Condensation of carbon in radioactive supernova gas.

Chemistry resulting in the formation of large carbon-bearing molecules and dust in the interior of an expanding supernova was explored, and the equations governing their abundances were solved numerically. Carbon dust condenses from initially gaseous carbon and oxygen atoms because energetic electrons produced by radioactivity in the supernova cause dissociation of the carbon monoxide molecules, which would otherwise form and limit the supply of carbon atoms. The resulting free carbon atoms enable carbon dust to grow faster by carbon association than the rate at which the dust can be destroyed by oxidation. The origin of presolar micrometer-sized carbon solids that are found in meteorites is thereby altered.

Astronomical Phenomena↗
PubMed1996

Elastase-induced hydrolysis of synthetic solid substrates: poly(ester-urea-urethane) and poly(ether-urea-urethane).

Human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) were incubated with two radiolabelled model poly(urethane), a poly(ester-urea-urethane) containing [14C]toluene diisocyanate ([14C]TDI), poly(caprolactone)(PCL) and ethylenediamine (ED), and a poly(ether-urea-urethane) containing [14C]TDI, poly(tetramethylene oxide) (PTMO) and ED. Ten-fold more radioactive carbon was released when PPE was incubated with [14C]TDI/PCL/ED than when HNE was used. The PPE-induced radioactive carbon release was significantly reduced by a specific elastase inhibitor. Ten-fold less radioactive carbon was released when [14C]TDI/PTMO/ED was incubated with PPE as compared to [14C]TDI/PCL/ED. Since neutrophils, which contain elastolytic activity, are present during the inflammatory response, the stability of biomaterials used in implanted devices may be affected.

Animals↗
PubMedDate not supplied

[Features of the effects of disaccharide structure of saccharose on kinetic parameters of hepatic lipid synthesis from glucose (mechanism of disaccharide effect)].

Effects of saccharose or invert sugar on kinetics of lipid synthesis in the rat liver were investigated using 1-14C-glucose as a precursor. The diet containing 30% of saccharose (of the total energy value) for 40 days was found to be sufficient to increase the radioactive carbon flux through total liver lipids more than twice, and through rapidly metabolized neutral lipids and phospholipids more than 4 and 3 times, consequently. On the contrary, when the invert sugar diet was used the radioactive carbon flux through total lipids in the liver was reduced up to 54% of the control level, the lowest radioactive carbon flux was observed through the rapidly metabolized fraction of phospholipids--6% of the control level, only. These changes were caused by the corresponding alterations in lipid synthesis constants.

Animals↗
PubMed1988

Biosynthesis of Territrems by Aspergillus terreus.

Different radioactive precursors were added to 8-day potato-dextrose liquid cultures of Aspergillus terreus 23-1. Territrems were isolated from chloroform extracts of the cultures at day 14 and purified by thin-layer chromatography and high-pressure liquid chromatography. The territrem B obtained was treated with alkaline hydrogen peroxide, and 3, 4, 5-trimethoxy benzoic acid was isolated from an ethyl acetate extract of the reaction mixture and purified by thin-layer chromatography and high-pressure liquid chromatography. By comparison of the specific radioactivities of territrem B and its cleaved aromatic product (disintegrations per minute per micromole of compound), it was demonstrated that the radioactivity of territrem B was located mainly on its aromatic moiety when [U-C]shikimate, l-[methyl-C]methionine, and l-[methyl-H]methionine were precursors; however, the radioactivity of territrem B was located mainly on its nonaromatic moiety when [2-C]mevalonate was the precursor. Mevinolin, a specific inhibitor of beta-hydroxyl beta-methyl glutaryl coenzyme A reductase, was shown to inhibit production of territrems by A. terreus 23-1. When [U-C]acetate was used as a precursor, mevinolin inhibited the incorporation of radioactive carbon into territrem but mevinolin did not inhibit incorporation of radioactive carbon from [2-C]mevalonate into territrem.

Journal Article↗
PubMed1985

The application of antibiotic bonding to the treatment of established vascular prosthetic infection.

We used surfactant-mediated antibiotic bonding to treat established vascular prosthetic infections in an animal model. The infrarenal aorta of dogs was replaced with a polytef (PTFE) graft locally contaminated with Staphylococcus aureus. Infected grafts were then replaced with control polytef or polytef bonded with benzylkonium chloride and penicillin G tagged with radioactive carbon, or polytef bonded with tridodecylmethylammonium chloride and penicillin G tagged with radioactive carbon. Both types of antibiotic-bonded grafts had significantly fewer infections than control grafts did. The labeled penicillin G remained bound to both groups of antibiotic-bonded grafts for at least three weeks. In a second group of studies, surfactant-treated polytef adsorbed parenterally administered labeled penicillin G in highly significant concentrations compared with control grafts. These studies suggest the possibility that human vascular prosthetic infection may be treated with an antibiotic-bonded graft.

Animals↗
PubMed1973

Effect of halofenate and clofibrate on growth and lipid synthesis in Saccharomyces cerevisiae.

Halofenate-free acid (HFA) inhibited the growth of Saccharomyces cerevisiae by 50% at a concentration of 0.34 mm. This inhibitory effect was prevented by addition of either oleate or acetate, but not by pyruvate. When cell growth was supported by oleate, HFA inhibited the incorporation of radioactive carbon from glucose-U-(14)C or pyruvate-2-(14)C into fatty acids and sterols. The incorporation of radioactive carbon into fatty acids and sterols from acetate-2-(14)C was unaffected by the compound. When cell growth was supported by either oleate or acetate, HFA inhibited the conversion of pyruvate-1-(14)C to (14)CO(2). These results suggest that HFA inhibits the conversion of pyruvate to acetate in yeast. Partially purified yeast pyruvate dehydrogenase was inhibited 50% by 5.5 mm HFA; however, the concentration required for 50% inhibition was considerably reduced when the enzyme was preincubated with the compound at room temperature. In a similar manner, the hypolipidemic agent clofibrate-free acid inhibited the growth of yeast by 50% at 3.0 mm. This inhibition was also prevented by acetate and not by pyruvate. In addition, clofibrate-free acid inhibited partially purified pyruvate dehydrogenase by 50% at a concentration of 37.0 mm.

Acetates↗
PubMed1974

Amino acid biosynthesis in the spirochete Leptospira: evidence for a novel pathway of isoleucine biosynthesis.

Radioactive carbon dioxide was incubated with growing cells of Leptospira interrogans serotypes semaranga and tarassovi, and the specific activities and distribution of the label within the cellular amino acids were determined. The origins of the carbon skeletons of all the acid-stable amino acids except isoleucine were found to be consistent with known biosynthetic pathways for these amino acids. Experiments using radioactive carbon dioxide and other tracers indicated that most of the isoleucine was synthesized by a pathway not involving threonine. The origin of the carbon skeleton of isoleucine consisted of two residues of pyruvate (carbons 2 and 3) and acetate of acetyl-coenzyme A by this pathway. Isotope competition studies indicated that the pathway was regulated by isoleucine. The results are discussed in relation to two proposed pathways of isoleucine biosynthesis involving citramalate as an intermediate.

Amino Acids↗
PubMed1983

Multiple pathways for isoleucine biosynthesis in the spirochete Leptospira.

Spirochetes of the genus Leptospira have previously been shown to use an unusual pathway to synthesize isoleucine. For reasons of convenience, we assume that only one unusual pathway is found in the genus, and we refer to it as the pyruvate pathway. We determined the distribution of this pyruvate pathway in representatives of the seven Leptospira DNA hybridization groups. Our method included labeling the representative strains with radioactive carbon dioxide and other radioactive precursors, fractionating the cells, and determining the specific activities (counts detected per nanomole) of the amino acids found in the protein fractions. On the basis of isoleucine biosynthesis, we found that the genus can be classified as follows: class I primarily, if not exclusively, uses the well-known threonine pathway; class II uses mostly the pyruvate pathway, with a minor amount of isoleucine being synthesized via the threonine pathway; and class III uses the pyruvate pathway exclusively. No relationship appears to exist between the degree of DNA hybridization and the classes of isoleucine biosynthesis. Although the precise intermediates on the pyruvate pathway are unknown, the origin of the carbon skeleton of isoleucine synthesized by this pathway is consistent with a borrowing of the leucine biosynthetic enzymes. However, we found that the pyruvate pathway is not controlled by leucine and that the two isoleucine pathways are independently regulated. Finding major and highly evolved multiple biosynthetic pathways of a specific amino acid within one genus is unique, and, conceivably, represents phylogenetic diversity within Leptospira.

Isoleucine↗
PubMed1972

Carbon monoxide balance in nature.

Consideration of the steady-state equations for stable carbon monoxide and for radioactive carbon monoxide in the troposphere leads to the conclusion that carbon monoxide is produced at a rate of 5x10(15) grams per year, a value some 25 times greater than the rate of carbon monoxide production from combustion. The concomitant residence time for carbon monoxide is 0.1 year, in agreement with a previous estimate of Weinstock. Hydroxyl radicals are shown to account for both the production of this large amount of carbon monoxide by methane oxidation and for its removal by carbon monoxide oxidation. The average concentration of hydroxyl radicals in the troposphere required to achieve this effect is 2.3x10(6) molecules per cubic centimeter, with a daytime concentration of twice that. Levy and McConnell, McElroy, and Wofsy have deduced concentrations of hydroxyl radicals in the troposphere of the same magnitude from purely photochemical considerations, in support of this model.

Air↗