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PubMed2001

Resistance to ACCase-inhibiting herbicides and isoproturon in UK populations of Lolium multiflorum: mechanisms of resistance and implications for control.

Herbicide-resistant Lolium multiflorum (Italian rye-grass) was first reported in the UK in 1993 and had been confirmed on 25 farms by 1999. In this study, resistance to five herbicides belonging to the aryloxyphenoxypropionate, cyclohexanedione and phenyl-urea classes was determined in six populations of L multiflorum from the UK under glasshouse and simulated field conditions. Glasshouse conditions tended to exaggerate the degree of resistance, but experiments performed in both environments detected resistance in four populations of L multiflorum. Four populations (Essex A1, Lincs A1, Wilts B1, Yorks A2) were resistant to diclofop-methyl, fluazifop-P-butyl, tralkoxydim and partially resistant to isoproturon, but only the population from Yorkshire (Yorks A2) showed resistance to cycloxydim. Biochemical analyses of acetyl coenzyme A carboxylase (ACCase) activity, oxygen consumption by thylakoids, diclofop metabolism and glutathione S-transferase activity showed that, in three of the resistant populations, an enhanced rate of herbicide metabolism conferred resistance. This is the first report world-wide of an enhanced metabolism mechanism of diclofop resistance in L multiflorum. In the Yorks A2 population, an insensitive ACCase was detected (target-site resistance) which also conferred cross-resistance to all of the other ACCase inhibitors investigated.

Acetyl-CoA Carboxylase↗
PubMed1985

Disruption of circadian rhythm of tissue respiration in Channa striatus by Metasystox.

Oxygen consumption of gill, brain and muscle tissues of Channa striatus exhibits a clearcut circadian rhythm with a maximum uptake at 18.00 h. Metasystox exposure decreased the oxygen consumption of all tissues. Maximum reduction is noted in gill followed by brain and muscle. The peak period of oxygen consumption is also eliminated in the pesticide-treated fish.

Animals↗
PubMed2004

Synthesis and cytotoxic activity of benzo[c][1,7] and [1,8]phenanthrolines analogues of nitidine and fagaronine.

Fagaronine and nitidine are natural benzo[c] phenanthridinium alkaloids, which display antileukemic activity. Both act as topoisomerase I and topoisomerase II inhibitors. The objective of the present study was to prepare noncharged isosters of these compounds, with replacement of the aromatic A ring by a pyridine ring, present in other topoisomerase I inhibitors. Various 7,8- and 8,9-dimethoxy and metylenedioxy benzo[c][1,7] and [1,8]phenanthrolines were readily synthesized by benzyne-mediated cyclization of the corresponding substituted N-(2-halobenzyl)-5-quinolinamines or 5-isoquinolinamines. In both series, compounds bearing oxygenated substituents at positions 8 and 9 exhibited cytotoxic properties towards L1210 murine leukemia cells, which may result from their capacities to intercalate into DNA. Topoisomerase I inhibition was observed for all active compounds.

Alkaloids↗
PubMed1991

3,4-Dihydroxyxanthone dioxygenase from Arthrobacter sp. strain GFB100.

Bacterial extradiol ring-fission dioxygenases play a critical role in the transformation of multiring aromatic compounds to more readily biodegradable aromatic or aliphatic intermediates. Arthrobacter sp. strain GFB100 utilizes an extradiol meta-fission dioxygenase, 3,4-dihydroxyxanthone dioxygenase (DHXD), in the catabolism of the three-ring oxygen heterocyclic compound xanthone. In this paper, we show that DHXD is a cytosolic enzyme, induced by growth on xanthone and maximally expressed during the stationary phase of growth. In addition, we characterize the DHXD activity in terms of its basic enzymological properties. 1,10-Phenanthroline and H2O2 treatments eliminated DHXD activity, indicating that the enzyme required Fe2+ ions for activity. Other divalent cations were either inhibitory or had no effect on activity. DHXD had a temperature optimum of 30 degrees C and a pH optimum of 7.0. DHXD followed typical saturation kinetics and had an apparent Km of 10 microM for 3,4-dihydroxyxanthone. The dye celestine blue served as a noncompetitive DHXD inhibitor (Ki, 5 microM). Several other structural analogs served neither as substrates nor inhibitors. DHXD was thermally labile at temperatures above 40 degrees C. The half-life for thermal DHXD inactivation was 5 min at 40 degrees C. DHXD activity was completely stable through one freeze-thaw cycle, and about 80% of the DHXD activity remained after 2 days of incubation at 0 degree C. The apparent tight binding of the Fe2+ cofactor to DHXD may be a factor contributing to the stability of this extradiol dioxygenase when it is stored.

Arthrobacter↗
PubMed1983

Preparation and stabilization of aqueous/ethanolic superoxide solutions.

Methods for the generation and stabilization of alkaline aqueous and/or ethanolic superoxide solutions have been developed utilizing either high energy ionizing radiation or vacuum-uv photolysis. These solutions can be used for the study of the reactivity of superoxide radical (O-2) and its conjugate acid the perhydroxyl radical (HO2) with other compounds over the entire pH range. Frozen, they can be kept at -196 degrees C for prolonged time periods with little loss in superoxide radical. As these solutions can be rendered free of molecular oxygen, studies of the reactivity of HO2/O-2 with oxygen-sensitive compounds under virtually anaerobic conditions are possible.

Chemical Phenomena↗
PubMed1980

Applicability of the phosphorus-31 (oxygen-17) nuclear magnetic resonance method in the study of enzyme mechanism involving phosphorus.

The phosphorus-31 (oxygen-17) [31P (17O)] NMR method [Tsai, M.-D. (1979) Biochemistry 18, 1448-1472] is tested for its general applicability by correlation with the line widths of the 17O NMR signals for the following compounds: trimethyl [17O4]phosphate (1), [17O4]phosphate (2), [alpha-17O2]adenosine 5'-(thiophosphate) (3), [alpha-17O, alpha beta-17O]-adenosine 5'-(1-thiotriphosphate) (4) [gamma-17O3]adenosine 5'-triphosphate (5), [alpha beta, beta gamma-17O2, beta-17O2]adenosine 5'-triphosphate (6), magnesium [gamma-17O3]adenosine 5'-triphosphate (7), and magnesium [alpha beta, beta gamma-17O2, beta-17O2]adenosine 5'-triphosphate (8). It is found that the line broadening effect of 17O on the 31P signals of the directly bonded 31P nuclei is present for all the functional groups in the above compounds which include examples of small 17O line widths (1 and 2), of intermediate 17O line widths (3, 5, and the nonbridge 17O of 4 and 6), and of very large 17O line widths (7, 8, and the bridge 17O of 4 and 6). On the basis of the established approximate relationship delta chi delta Q approximately aJ2, where delta chi and delta Q are the 31P and 17O line widths, respectively, of the 31P-17O groups, alpha is a constant, and J is the 31P-17O coupling constant, the results suggest that for most of the phosphate derivatives of biochemical interest, the line broadening effect of 17O should be present and detectable; i.e., delta chi should be larger than the limiting value (approximately 20 Hz). It is also found that Mg2+ causes the 17O signal of 5 and 6 to broaden (delta Q increases), which in turn causes the 31P signal to sharpen (delta chi decreases). The finding suggests that the 31P (17O) NMR methods, in combination with 17O NMR, could become a tool to study diamagnetic metal ion-nucleotide interactions.

Adenosine Triphosphate↗
PubMed2006

Persistent S-nitrosation of complex I and other mitochondrial membrane proteins by S-nitrosothiols but not nitric oxide or peroxynitrite: implications for the interaction of nitric oxide with mitochondria.

S-nitrosation of mitochondrial proteins has been proposed to contribute to the pathophysiological interactions of nitric oxide (NO) and its derivatives with mitochondria but has not been shown directly. Furthermore, little is known about the mechanism of formation or the fate of these putative S-nitrosothiols. Here we have determined whether mitochondrial membrane protein thiols can be S-nitrosated on exposure to free NO from 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA-NONOate) by interaction with S-nitrosoglutathione or S-nitroso-N-acetylpenicillamine (SNAP) and by the NO derivative peroxynitrite. S-Nitrosation of protein thiols was measured directly by chemiluminescence detection. S-Nitrosoglutathione and S-nitroso-N-acetylpenicillamine led to extensive protein thiol oxidation, with about 30% of the modified protein thiols persistently S-nitrosated. In contrast, there was no protein thiol oxidation or S-nitrosation on exposure to 3,3-bis (aminoethyl)-1-hydroxy-2-oxo-1-triazene. Peroxynitrite extensively oxidized protein thiols but produced negligible amounts of S-nitrosothiols. Therefore, mitochondrial membrane protein thiols are S-nitrosated by preformed S-nitrosothiols but not by NO or by peroxynitrite. These S-nitrosated protein thiols were readily reduced by glutathione, so S-nitrosation will only persist when the mitochondrial glutathione pool is oxidized. Respiratory chain complex I was S-nitrosated by S-nitrosothiols, consistent with it being an important target for S-nitrosation during nitrosative stress. The S-nitrosation of complex I correlated with a significant loss of activity that was reversed by thiol reductants. S-Nitrosation was also associated with increased superoxide production from complex I. These findings point to a significant role for complex I S-nitrosation and consequent dysfunction during nitrosative stress in disorders such as Parkinson disease and sepsis.

Animals↗
PubMed2006

Monitoring the effect of mild hyperthermia on tumour hypoxia by Cu-ATSM PET scanning.

PURPOSE: Mild hyperthermia can improve tumour oxygenation and enhance radiosensitivity. Imaging the hypoxic fraction of a tumour can guide hyperthermia treatment planning and facilitate treatment optimization. 64Cu-ATSM (Copper-diacetyl-bis(N4-methylthiosemicarbazone)) is a positron emitting compound that has been demonstrated to have rapid uptake and selective retention in hypoxic cells and has been used for imaging human and animal tumours. The purpose of the present report is to establish methodology that will allow one to use Cu-ATSM PET scanning to detect the impact of hyperthermia on tumour physiology in as little time as possible. MATERIALS AND METHODS: EMT6 tumours (mouse mammary carcinoma) were implanted into the subcutaneous tissue of both thighs of 10 BALB/c mice (one heated, one control tumour per animal). The target thermal dose was 41.5 degrees C x 45 min. Without interrupting heating, 64Cu-ATSM (mean activity 1.8 mCi) was then injected and serial PET scans were obtained. In a sub-group of four animals, a low administered activity (approximately 0.3 mCi) 64Cu-ATSM scan was also conducted before heating to permit a direct comparison of the effects of hyperthermia on the same tumours. In another sub-group of five animals, a low activity (approximately 0.3 mCi) 64Cu-PTSM (pyruvaldehyde-bis(N*-methylthiosemicarbazone)) scan was conducted before heating, to confirm a posited correlation between perfusion and early 64Cu-ATSM uptake. RESULTS: This study corrected for perfusion differences by dividing tumour uptake by the average early (first minute) uptake ('self-normalized uptake'). The 10 heated tumours showed a significantly (p = 0.007) lower self-normalized uptake than control tumours by 2 min. For the four mice with low activity Cu-ATSM scans performed before hyperthermia, the tumours to be heated demonstrated self-normalized uptake consistent with the unheated control tumours and which departed significantly (p < or = 0.02) from their post-hyperthermia scans by 5 min. Comparisons between scans and needle electrode surveys were performed in an additional four animals with eight tumours. For technical reasons electrode surveys were done after the end of hyperthermia-and, therefore, these animals also had comparison scans taken after hyperthermia. Reduced self-normalized uptake on scans was associated with increased pO2 on electrode surveys. These data also suggested a substantial degradation of the effect on tumour hypoxia by approximately 15-45 min after the end of mild hyperthermia. CONCLUSION: Short imaging times of approximately 5 min with modest (approximately 4-10) numbers of mice can discriminate the effects of mild hyperthermia on tumour physiology. The long-term objective is to use this tool to identify as short and mild a hyperthermia session as possible.

Animals↗
PubMed1981

Differential effects of methacholine and antigen challenge on gas exchange in allergic subjects.

In order to better characterize the differential effects of nonspecific and specific (antigen) bronchial challenge on gas exchange, seven ragweed-sensitive subjects with a history of asthma underwent progressive inhalation challenge with methacholine and ragweed extract on two different days. For comparable severity of bronchospasm (mean specific airway conductance 0.05 sec-1cm-1H2O for methacholine and 0.06 sec-1cm-1H2O for ragweed), there was a greater decrease in mean arterial oxygen saturation after ragweed (4.7%) than after methacholine challenge (2.7%) (p less than 0.05). While this was not accompanied by differences in static lung volumes, the density-dependent index decreased by 19% after ragweed (p less than 0.001) but remained unchanged after methacholine challenge. These results suggest that a greater involvement of peripheral airways in the bronchospastic response is, at least in part, responsible for the greater decrease in arterial oxygen saturation after ragweed challenge.

Adult↗
PubMed2004

Dioxygen activation by a low-valent cobalt complex employing a flexible tripodal N-heterocyclic carbene ligand.

The novel versatile cobalt(I) tris-carbene complex [(TIMEN(xyl))Co]Cl (1) (where TIMEN = (tris[2-(3-arylimidazol-2-ylidene)ethyl]amine) reacts with CO, one-electron oxidizers such as CH(2)Cl(2), and O(2) to yield the cobalt complexes [(TIMEN(xyl))Co(CO)]Cl (2), [(TIMEN(xyl))Co(Cl)]Cl (3), and peroxo species [(TIMEN(xyl))Co(O(2))](BPh(4)) (5). All new complexes were fully characterized by (1)H NMR, UV/vis, and IR spectroscopy as well as superconducting quantum interference device (SQUID) magnetization measurements and single-crystal X-ray crystallography. The nucleophilic character of the eta(2)-bound dioxygen ligand in 5 was confirmed by density functional theory (DFT) studies and allows for oxygen-transfer reactions with electron-deficient organic substrates, such as benzoyl chloride.

Cobalt↗
PubMed1991

Carboxylated zinc-phthalocyanines--II. Dimerization and singlet molecular oxygen sensitization in hexadecyltrimethylammonium bromide micelles.

The dimerization of the diamide of zinc-tetracarboxyphthalocyanine was studied spectroscopically in hexadecyltrimethylammonium bromide (CTAB) micelles at surfactant concentrations from 0.026 to 0.1 M and dye concentrations between 0.1 and 10 microM. The apparent dimerization constant in CTAB 0.1 M is 8.6 x 10(5) M-1, while the intramicellar dimerization constant is 1.8 x 10(3). The dimer absorption spectrum was also obtained. Singlet molecular oxygen sensitization was studied by steady state photolysis using 1,3-diphenylisobenzofurane as scavenger in 0.1 M CTAB. The usual sensitization mechanism is extended to include dimer reactions. Singlet molecular oxygen sensitization yields for monomer and dimer in the micelles are 0.7 and 0.1, respectively. With the reported values it is possible to calculate the average yield of singlet molecular oxygen production at any surfactant and dye concentrations.

Cetrimonium↗