共查询到20条相似文献,搜索用时 15 毫秒
1.
Fumiaki Nakatsubo Ian D. Reid T.Kent Kirk 《Biochemical and biophysical research communications》1981,102(1):484-491
The possible involvement of singlet oxygen (1O2) in the degradation of lignin by was examined. Ligninolytic cultures and photochemically generated 1O2 gave the same oxidation products from the lignin substructure model compound 1,2-bis(3-methoxy-4-alkoxyphenyl)propan-1,3-diol. Fluorescence and near UV absorbance of the specific 1O2 trapping agent anthracene-9,10-bisethanesulfonic acid (AES) disappeared in ligninolytic cultures, indicating that 1O2 was produced. AES strongly inhibited oxidation of 14C-lignin, but not 14C-glucose, to 14CO2 in cultures, and also strongly suppressed oxidation of the model compound. These results indicate the 1O2 plays an integral role in lignin biodegradation. 相似文献
2.
Robert E. Lynch Barry C. Cole 《Biochemical and biophysical research communications》1980,96(1):98-105
Superoxide dismutase and catalase were not detected in . and several other species of some of which consume oxygen and secrete H2O2. . in suspension formed O2? in the presence of NADH and flavins and extracts of . formed O2? in the presence of either NADH or NADPH. The lack of superoxide dismutase in . could not be attributed to superoxide dismutase in the complex medium in which the organisms were grown because organisms grown in medium in which the superoxide dismutase had been inactivated by heat still contained undetectable amounts. Mycoplasmas appear to be an exception to the rule that organisms which consume O2 synthesize superoxide dismutase. 相似文献
3.
M S Balakrishnan T R Sharp J J Villafranca 《Biochemical and biophysical research communications》1978,85(3):991-998
Oxygen-18 exchange out of [18O]Pi catalyzed by Mg2+-activated unadenylated glutamine synthetase from was followed by 31P-NMR in the presence of the other substrates, ADP and L-glutamine. The pattern of the in the species P18O4, P18O316O1, P18O216O2, P18O116O3, P16O4 during the exchange followed a binomial distribution consistent with indiscriminate removal of any of the four oxygens of Pi. The rate constant for exchange was 410±40 min?1 while the rate constant for net reaction (ATP formation) was 62±4 min?1. Thus exchange proceeds ~7 times faster than net reaction, a finding in accord with that of Stokes and Boyer ( (1976) , 5558) for the Mn2+-activated adenylylated glutamine synthetase. A model for the overall catalytic events first derived from rapid kinetic fluorescence experiments (Rhee and Chock, Proc. Natl. Acad. Sci. USA, (1976) , 476) was successfully used to fit the oxygen exchange data in this paper. 相似文献
4.
Eleanor G. Rogan Alaeddin Hakam Ercole L. Cavalieri 《Chemico-biological interactions》1983,47(1):111-122
Activation of polycyclic aromatic hydrocarbons (PAH) by horseradish peroxidase (HRP) with H2O2 has been studied as a model system for one-electron oxidation. This peroxidase has been used to catalyze binding of (BP-6-CH3) to DNA, which was purified, hydrolyzed to deoxyribonucleosides and analyzed by high pressure liquid chromatography (HPLC). The predominant hydrocarbon-DNA adduct observed was identified as BP-6-CH3 bound at the 6-methyl group to the 2-amino group of dG, confirming that activation by HRP occurs by one-electron oxidation. When DNA from mouse skin treated in vivo with [14C]BP-6-CH3 was purified, hydrolyzed and analyzed by HPLC, a profile was observed which was qualitatively similar to that from the peroxidase system. In particular, the identified adduct with the hydrocarbon bound at the 6-methyl group to the 2-amino group of dG was obtained. These results demonstrate that one-electron oxidation is the mechanism of activation by HRP for aromatic hydrocarbons and indicate that the same mechanism may occur in mouse skin, a target tissue for hydrocarbon carcinogenesis. 相似文献
5.
NH2OH-treated, non-water-splitting chloroplasts can oxidize H2O2 to O2 through Photosystem II at substantial rates (100–250 μequiv · h?1 · mg?1 chlorophyll with 5 mM H2O2) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H2O2 → Photosystem II → dimethylquinone reaction supports phosphorylation with a ratio of 0.25–0.35 and proton uptake with values of 0.67 (pH 8)–0.85 (pH 6). These are close to the value of 0.3–0.38 and the values of 0.7–0.93 found in parallel experiments for the H2O → Photosystem II → dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor → Photosystem II → dibromothymoquinone (→O2) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I?, ferrocyanide). 相似文献
6.
Charles L. Swendsen J.Marshall Ellis Floyd H. Chilton Joseph T. OFlaherty Robert L. Wykle 《Biochemical and biophysical research communications》1983,113(1):72-79
Rabbit peritoneal neutrophils incorporated [14C]arachidonic acid into seven molecular species of choline-containing phosphoglycerides. These 2-[14C]arachidonoyl species differed with respect to the alkyl ether or acyl residue bound at the -1 position; four of the seven were ether-linked. Stimulation with calcium ionophore A23187 induced a proportionate release of arachidonate from all seven molecular species: 40% of the released arachidonate came from alkyl ether species. Thus, 1--alkyl-2-arachidonoyl--glycero-3-phosphocholine (GPC) is a significant source of metabolizable arachidonic acid. Since 1--alkyl-2-lyso-GPC is the metabolic precussor of platelet activating factor, these results further interrelate pathways forming arachidonate metabolites and platelet activating factor; they also supply a rationale for the observation that both classes of stimuli form concomitantly during cell activation. 相似文献
7.
A nuclear exoribonuclease from Novikoff ascites cells was used to study the hydrolysis of single-stranded heteropolymers containing [14C]adenylic acid and either uridylic acid or cytidylic acid and heteropolymers of [14C]adenylic acid and one of the corresponding 2′--methylated nucleotides. The results of these studies indicate that both the rate and extent of hydrolysis are greatly inhibited by the presence of 2′--methylated nucleotides. Restriction of exonuclease activity by 2′--methylated nucleotides provides a possible mechanism for rRNA processing. 相似文献
8.
Recently, it was suggested that the measured rate of reduction of ferricyto chrome by O?2 below pH 8, was too high in the presence of high concentrations of formate (Koppenol, W.H., Van Buuren, K.J.H., Butler J. and Braams, R. (1976) Biochim. Biophys. Acta 449, 157–168).The high values were attributed to the presence of impurities of copper, which compete for O?2. This assumption is consistent with either a decrease in the reduction yield of ferricytochrome in the presence of copper, or with a very fast reaction of Cu(I) with ferricytochrome .It was previously shown by us and by others that the reduction yield of ferricytochrome by O?2 is 100%. We measured the rate of reduction of ferricytochrome by Cu(I), and found that this reaction is slow: .Therefore, our results rule out the possibility that below pH 8 copper impurities affect the measured rate constant of the reduction of ferricytochrome by O?2. 相似文献
9.
[4-14C]Cholesterol was incubated with an adrenocortical preparation in the presence of 16O2 and 18O2 devoid of significant 16O18O. Isolated (20R,22R)-20,22-dihydroxycholesterol was converted to a trimethylsilyl derivative and analyzed by gas chromatography - mass spectrometry to determine the isotope distribution of the oxygen atoms at C-20 and C-22. The ions of 289, 291, and 293 (comprising the C8 C-20 to C-27 side-chain and containing, respectively, 16O2, 16O18O, and 18O2) exhibited a binomial distribution indicating that the oxygen atoms of the vicinal glycol were drawn at random from the atomic pool of the oxygen molecules. If both side-chain hydroxyl groups had originated from the atoms of the same oxygen molecule, the ion of 291 would have been absent. 相似文献
10.
14C-Sterigmatocystin isolated from cultures of supplemented with (1-14C)acetate was shown to be efficiently converted to aflatoxin B1 by the resting mycelium of . The experimental results may indicate a biosynthetic pathway leading from 5-hydroxysterigmatocystin to sterigmatocystin and then to aflatoxin B1. 相似文献
11.
C.R. Pace-Asciak M.C. Carrara L. Levine K.C. Nicolaou 《Prostaglandins & other lipid mediators》1980,20(6):1053-1060
Immunoglobulins raised against 5,6-dihydro PGI2 crossreact with PGI2. When infused into the rat, these immunoglobulins are capable of I) neutralising the vasodepressor effects (bolus or continuous infusion) of exogenous PGI2, 2) blocking the catabolism of exogenous 3H-PGI2 and prolonging its life-time in the circulation (t approx 60 min) while that of 3H-PGE2 is unaffected, 3) trapping an endogenously produced substance which after extraction from blood and dissociation from the ligand-antibody complex, is immunoreactive with 6-keto PGF1α-specific antiserum. Yet the anti-5,6-dihydro PGI2 immunoglobulins have no effect on resting arterial blood pressure both in the normotensive and spontaneously hypertensive rat. These experiments indicate that endogenously produced PGI2 does not play a significant role in blood pressure control although in combination with other vasodilators it could still participate in the regulation of vascular tone at a local level. 相似文献
12.
O2 uptake in spinach thylakoids was composed of ferredoxin-dependent and -independent components. The ferredoxin-independent component was largely 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) insensitive (60%). Light-dependent O2 uptake was stimulated 7-fold by 70 μM ferredoxin and both uptake and evolution (with O2 as the only electron acceptor) responded almost linearly to ferredoxin up to 40 μM. NADP+ reduction, however, was saturated by less than 20 μM ferredoxin. The affinity of O2 uptake for for O2 was highly dependent on ferredoxin concentration, with of less than 20 μM at 2 μM ferredoxin but greater than 60 μM O2 with 25 μM ferredoxin. O2 uptake could be suppressed up to 80% with saturating NADP+ and it approximated a competitive inhibitor of O2 uptake with a Ki of 8–15 μM. Electron transport in these thylakoids supported high rates of photophosphorylation with NADP+ (600 μmol ATP/mg Chl per h) or O2 (280 μmol/mg Chl per h) as electron acceptors, with ratios of 1.15–1.55. Variation in ratios with ferredoxin concentration and effects of antimycin A indicate that cyclic electron flow may also be occurring in this thylakoid system. Results are discussed with regard to photoreduction of O2 as a potential source of ATP in vivo. 相似文献
13.
Olga Genbačev Marija Ratković Miodrag Krainčanić Vojin Šulović 《Prostaglandins & other lipid mediators》1977,13(4):723-733
The biosynthesis of placental proteins and placental lactogen (HPL) was studied in 10–12 week, 16–18 week and term human placenta in the presence and absence of PGE2α. The highest 14C-leucine incorporation was detected in 10 to 12 weeks old placentas. Addition of PGE2α to the induction medium depressed the rate of incorporation of 14C-leucine into placental proteins on a dose dependent manner. Placentas most sensitive to this action of PGE2α were those obtained at 18 weeks gestation followed by placentas at term. application of PGE2α for tharapeutic induction of abortions resulted in the marked inhibition of placental protein synthesis . 相似文献
14.
The relationship between cell fusion, DNA synthesis and the cell cycle in cultured embryonic normal and dysgenic () mouse muscle cells has been determined by autoradiography. The experimental evidence shows that the homozygous mutant myotubes form by a process of cell fusion and that nuclei within the myotubes do not synthesize DNA or undergo mitotic or amitotic division. The duration of the total cell cycle and its component phases was statistically the same in 2-day normal and mutant () myogenic cultures with the approximate values: T, 21.5 hr; G1, 10.5 hr; S, 7.5 hr; and G2, 2.5 hr. In both kinds of cultures, labeled nuclei appeared in myotubes 15–16 hr after mononucleated cells were exposed to [3H]thymidine, and the rate of incorporation of labeled nuclei into multinucleated muscle cells was comparable in control and dysgenic cultures. Thus, homozygous muscle cells in culture are similar to control cells with respect to their mechanism of myotube formation and the coordinate regulation of DNA synthesis and the cell cycle during myogenesis. 相似文献
15.
Robert C. Richmond John D. Zimbrick 《Biochemical and biophysical research communications》1975,64(1):391-398
Cells of C thy?321 are examined for thymine residue release from DNA following gamma-irradiation from 5 to 15 krad. Experimental conditions are designed to inhibit enzyme activity that might promote base residue release. Enzyme action is restricted in order to assess the physicochemical action of radiation on cellular DNA, and to this end irradiation is done under O2, N2, and N2O saturating conditions. Both thymine and thymidine release from bacterial DNA are detected and quantitated, and three oxygen effects are noted in comparing yields of these products. No difference in effect is observed between N2 and N2O gassing conditions, suggesting that the hydroxyl radical has little effect on thymine or thymidine release from irradiated DNA . 相似文献
16.
Richard Moskala C.Channa Reddy Robert D. Minard Gordon A. Hamilton 《Biochemical and biophysical research communications》1981,99(1):107-113
In the conversion of -inositol to D-glucuronic acid catalyzed by -inositol oxygenase only one atom of 18O from 18O2 is incorporated into the product, and it is found exclusively in the carboxyl group. Control experiments indicate that under the reaction conditions no exchange of solvent oxygens with D-glucuronate occurs. To avoid exchange during isolation and analysis the oxygenase product was enzymically reduced to L-gulonate and isolated in that form. The results eliminate one possible mechanism for the oxygenase reaction, but are consistent with two others which seem chemically reasonable. 相似文献
17.
The relative effectiveness of oxidizing (.OH, H2O2), ambivalent (O2?) and reducing free radicals (e? and CO2?) in causing damage to membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase of resealed erythrocyte ghosts has been determined. The rates of damage to membranebound glyceraldehyde-3-phosphate dehydrogenase ((enz)) were measured and the rates of damage to membranes ((mb)) were assessed by measuring changes in permeability of the resealed ghosts to the relatively low molecular weight substrates of glyceraldehyde-3-phosphate dehydrogenase. Each radical was selectively isolated from the mixture produced during gamma-irradiation, using appropriate mixtures of scavengers such as catalase, superoxide dismutase and formate. .OH, O2? and H2 O2 were approximately equally effective in inactivating membrane-bound glyceraldehyde-3-phosphate dehydrogenase, while e? and CO2? were the least effective. (enz) values of O2? and H2O2 were 10-times and of .OH 15-times that of e?. (mb) values were quite similar for e? and H2O2 (about twice that of O2?), while that of .OH was 3-times that of O2?. Hence, with respect to (mb): , and with respect to (enz): . The difference between the effectiveness of the most damaging and the least damaging free radicals was more than 10-fold greater in damage to the enzyme than to the membranes. Comparison between H2O2 added as a chemical reagent and H2O2 formed by irradiation showed that membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase were relatively inert to reagent H2O2 but markedly susceptible to the latter. 相似文献
18.
The rate of reaction of ferro- and ferricytochrome c (C(II) and C(III)) with ferri- and ferrocyanide and of C(III) with O2? and CO2? was determined in H2O and in 2H2O in the temperature range 5–35 °C. No isotope effect was evident in any of the reductions of C(III); the apparent energy of activation was identical in H2O and 2H2O. An isotope effect with , depending on pH for instance was observed in the oxidation of C(II), in the slow phase of oxidation which involves conformational changes. An interpretation (supported by evidence from previous work) involving water molecules in the close vicinity of the reaction site on the protein is discussed. 相似文献
19.
Luis O. Rodriguez Sidney M. Hecht 《Biochemical and biophysical research communications》1982,104(4):1470-1476
Consistent with a recent literature report (Repine, J. E. (1981) , 1001–1003), the release of [3H]-thymine from PM-2 DNA by Fe(II)-H2O2-generated ·OH was suppressed by dimethyl sulfoxide. In contrast, DMSO did not affect [3H]-thymine release mediated by Fe(II)-bleomycin. Under aerobic conditions in the presence of -butyl phenylnitrone, Fe(II)-BLM produces an epr signal that has been presumed to arise by transfer of ·OH or from the “active complex” of bleomycin to the spin trap. Remarkably, high concentrations (80 mM) of PBN had no effect on the ability of Fe(II)-BLM to solubilize [3H]-thymine, although the ability of authentic ·OH to degrade DNA was completely suppressed under these condition. The suproxide dismutase catalyst tetrakis(4-N-methylpyridyl)porphineiron(III) also failed to suppress BLM-mediated DNA degradation. Moreover, the epr signal observed with 1.6 mM Fe(II)-BLM in the presence of 80 mM PBN was found to be much less intense than that produced by 1.6 mM Fe(II) and 290 mM H2O2, but equivalent in intensity to that obtained with 45 mM Fe(II) and exoess H2O2. We conclude that the fragmentation of DNA produced by Fe(II)-BLM can be due neither to free ·OH nor to . We suggest that DNA degradation is initiated by an “active complex” consisting of BLM, metal and oxygen that functions by abstracting H· from susceptible sites on DNA. 相似文献
20.
Jaime Mas Esteban Celis Enrique Piña Aurora Brunner 《Biochemical and biophysical research communications》1974,61(2):613-620
It was found that the difference in the partial pressure of oxygen (pO2) resulting from the distinct altitude over the sea level, between Baltimore, Md., USA and Mexico City, about 2,240 meters, is sufficient to cause variance in conjugation frequency in two haploid strains of .Further studies confirm that sexual conjugation in is highly sensitive to changes in the pO2. Ergosterol which depends on O2 for its biosynthesis, stimulates the mating process, as does the ergosterol precursor, squalene. Ergosterol and O2 effects were found to be additive, suggesting that O2 may influence conjugation in more than one way. Culture, storage and transfer frequency modify both, mating efficiency and the response to O2 and lipid supplement. 相似文献