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1.
Agonist-specific desensitization of prostaglandin I2-stimulated (PGI2)1 adenosine 3′:5′-monophosphate (cyclic AMP) accumulation can be demonstrated in intact human foreskin fibroblasts (HFF) following a single exposure to PGE1 or a stable PGI2 analog (nitrilo-PGI2). A single PGI2-stimulation of HFF cells does not result in desensitization. Continuous re-addition of PGI2 over a 4 hr period does induce desensitization to subsequent PGI2-stimulation. HFF cells that are desensitized to PGI2 are also desensitized to PGE1 or nitrilo-PGI2 stimulation indicating that these agonists share a common adenylate cyclase complex. Desensitization to PGI2 can be measured after a 60 min, but not after a 30 min, exposure to PGE1 or nitrilo-PGI2. Once HFF cells are desensitized, a 12–24 hr period is required for the recovery of PGI2 sensitivity.The adenylate cyclase in membranes prepared from intact cells that were preincubated with PGE1 is also desensitized to subsequent PGI2-stimulation. Preincubation of cells with PGI2 does not induce desensitization of PGI2-stimulated adenylate cyclase. These data suggest that HFF cells must be constantly exposed to a biologically active prostaglandin for desensitization to occur. The intrinsic chemical lability of PGI2 may be a biochemical protection mechanism against desensitization in cells that normally respond to PGI2. 相似文献
2.
Oxygen inhibition of photosynthesis and CO2 evolution during photorespiration were compared in high CO2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O2, which appeared to be competitive and similar in magnitude to that in higher C3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO2 cells increased while the O2 effect declined. Photorespiration, measured as the difference between 14CO2 and 12CO2 uptake, was much greater and sensitive to O2 in high CO2 cells. Some CO2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O2. True photosynthesis was not affected by O2 in either case. The data indicate that the difference between high CO2 and air-grown algae could be attributed to the magnitude of CO2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae. 相似文献
3.
Congzhi Wang Xiuhui Zhang Yang Bai Fengxin Gao Qianshu Li 《Journal of molecular modeling》2013,19(8):3077-3086
Theoretical studies on the cyclopentadienyliron chlorides Cp2Fe2Cl n (n?=?6???1) with iron in the formal oxidation states from +1 to +4 indicate that all the high-spin species are predicted to be the lowest energy structures and they are paramagnetic complexes with magnetic moments between 2.8μ B and 5.9μ B. The mixed oxidation state derivatives with odd number of chloride atoms have larger magnetic moments than other species. In addition to Cp2Fe2Cl, which has the largest magnetic moment, these high-spin species have terminal Cp rings and bridging Cl atoms up to a maximum of two bridges. The Cp2Fe2Cl4, Cp2Fe2Cl3 and Cp2Fe2Cl2 derivatives are predicted to be thermodynamically stable molecules with respect to exothermic reactions for the loss of one Cl atom from Cp2Fe2Cl n . Moreover, the lowest energy Cp2Fe2Cl n (n?=?3, 4) derivatives can be derived by the oxidative addition reactions of Cp2Fe2Cl n?2 + Cl2 → Cp2Fe2Cl n . Figure
Molecular structures for Cp2Fe2Cln (n?=?6-1) 相似文献
4.
Using density functional theory calculations, we investigated properties of a functionalized BC2N nanotube with NH3 and five other NH2-X molecules in which one of the hydrogen atoms of NH3 is substituted by X = ?CH3, ?CH2CH3, ?COOH, ?CH2COOH and ?CH2CN functional groups. It was found that NH3 can be preferentially adsorbed on top of the boron atom, with adsorption energy of ?12.0 kcal mol?1. The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the functional groups. The adsorption energies are calculated to be in the range of ?1.8 to ?14.2 kcal mol?1, and their relative magnitude order is found as follows: H2N(CH2CH3) > H2N(CH3) > NH3 > H2N(CH2COOH) > H2N(CH2CN) > H2N(COOH). Overall, the functionalization of BC2N nanotube with the amino groups results in little change in its electronic properties. The preservation of electronic properties of BC2N coupled with the enhancement of solubility renders their chemical modification with either NH3 or amino functional groups to be a way for the purification of BC2N nanotubes. 相似文献
5.
Gas production by Chlamydomonas moewusii in the light has been followed by manometric techniques during the adaptation to anaerobiosis. The only detectable gases produced are CO2 and H2 CO2 is produced at a rather constant rate whereas H2 evolution increase with time. This increase of H2 evolution during the adaptation period can be inhibited by cycloheximide and by chloral hydrate, two inhibitors of protein synthesis. If the inhibitors are added to already adapted cells there is no effect on H2 evolution. Adapted cell suspensions are sensitive to oxygen. Incubation under O2 for 10 min inhibits the H2 evolution to 100%. After removal of oxygen the capability to evolve H2 can be restored only by a new adaptation period. This second adaptation to H2 evolution can also be inhibited by cycloheximide. 相似文献
6.
7.
T. Ramasarma Anand Swaroop W. MacKellar F. L. Crane 《Journal of bioenergetics and biomembranes》1981,13(5-6):241-253
The oxidation of NADH by mouse liver plasma membranes was shown to be accompanied by the formation of H2O2. The rate of H2O2 formation was less than one-tenth the rate of oxygen uptake and much slower than the rate of reduction of artificial electron acceptors. The optimum pH for this reaction was 7.0 and theK
m value for NADH was found to be 3×10–6 M. The H2O2-generating system of plasma membranes was inhibited by quinacrine and azide, thus distinguishing it from similar activities in endoplasmic reticulum and mitochondria. Both NADH and NADPH served as substrates for plasma membrane H2O2 generation. Superoxide dismutase and adriamycin inhibited the reaction. Vanadate, known to stimulate the oxidation of NADH by plasma membranes, did not increase the formation of H2O2. In view of the growing evidence that H2O2 can be involved in metabolic control, the formation of H2O2 by a plasma membrane NAD(P)H oxidase system may be pertinent to control sites at the plasma membrane. 相似文献
8.
Reactions of alkanolamines [R1R2NXOH; R1 = H, CH3, C2H5; R2 = H, CH3, C2H5 and X = -CH2CH2-, -CH2CH2CH2-, -CH2CHCH3, -C6H4CH2CH2-] with aluminium isopropoxide in different molar ratios (1 to 3) yield compounds of the type Al(OPri)3?n(OXNR1R2)n, where ‘n’ can be 1, 2 and 3. Most of the derivatives are distillable liquids, soluble in common organic solvents and susceptible to hydrolysis even by atmospheric moisture. The new derivatives are characterized by elemental analysis, IR and 1H NMR spectra. Molecular weight measurements of Al(OPri)3?n(OXNR1R2)n reveal them to be tetrameric in nature. 相似文献
9.
Matthew I. Jackson Hannah F. Fields Timothy S. Lujan Megan M. Cantrell Joseph Lin Jon M. Fukuto 《Archives of biochemistry and biophysics》2013
Nitroxyl (HNO) possesses unique and potentially important biological/physiological activity that is currently mechanistically ill-defined. Previous work has shown that the likely biological targets for HNO are thiol proteins, oxidized metalloproteins (i.e. ferric heme proteins) and, most likely, selenoproteins. Interestingly, these are the same classes of proteins that interact with H2O2. In fact, these classes of proteins not only react with H2O2, and thus potentially responsible for the signaling actions of H2O2, but are also responsible for the degradation of H2O2. Therefore, it is not unreasonable to speculate that HNO can affect H2O2 degradation by interacting with H2O2-degrading proteins possibly leading to an increase in H2O2-mediated signaling. Moreover, considering the commonality between HNO and H2O2 biological targets, it also seems likely that HNO-mediated signaling can also be due to reactivity at otherwise H2O2-reactive sites. Herein, it is found that HNO does indeed inhibit H2O2 degradation via inhibition of H2O2-metaboilizing proteins. Also, it is found that in a system known to be regulated by H2O2 (T cell activation), HNO behaves similarly to H2O2, indicating that HNO- and H2O2-signaling may be similar and/or intimately related. 相似文献
10.
B Poole 《Journal of theoretical biology》1975,51(1):149-167
Rat liver peroxisomes are membrane-bounded organelles containing catalase and oxidases producing H2O2. Diffusion effects in the metabolism of H2O2 and the physiological significance of the structure of peroxisomes are explored on the basis of two models. Model I considers the liver cell as consisting of two rapidly mixed compartments, the peroxisomal contents and the rest of the cell, separated by a membrane. On the basis of model I, it is concluded that in order to maintain a minimal H2O2 concentration in the cytoplasm, there must be an H2O2 destroying system in the cytoplasm, but the capacity of this system need be only a small fraction of that of the catalase in the peroxisomes. Model II takes account of the detailed morphology of peroxisomes and includes the effect of peroxisomal membrane permeability to H2O2 and H2O2 diffusion inside and outside the peroxisomes. On the basis of previously published experimental data and model II, it is concluded that the latency of catalase activity in intact peroxisomes is due chiefly to a permeability barrier to H2O2 at the peroxisomal membrane rather than to a restriction of H2O2 diffusion within the peroxisomes. Peroxisomes are calculated to be very efficient at destroying the H2O2 produced within them, whether the H2O2 is produced in the catalase-free core or in the catalase-containing matrix. Less than 2% of the H2O2 produced in peroxisomes leaves the particles. The efficiency of H2O2 trapping is the consequence of the membrane permeability barrier. A similar H2O2 trapping efficiency could be achieved by particles without a membrane barrier only if H2O2 diffusion within such particles were reduced by many orders of magnitude. 相似文献
11.
O. Cantoni G. Brandi G.F. Schiavano A. Albano F. Cattabeni 《Chemico-biological interactions》1989,70(3-4)
The toxicity of H2O2 in Escherichia coli wild type and superoxide dismutase mutants was investigated under different experimental conditions. Cells were either grown aerobically, and then treated in M9 salts or K medium, or grown anoxically, and then treated in K medium. Results have demonstrated that the wild type and superoxide dismutase mutants display a markedly different sensitivity to both modes of lethality produced by H2O2 (i.e. mode one killing, which is produced by concentrations of H2O2 lower than 5 mM, and mode two killing which results from the insult generated by concentrations of H2O2 higher than 10 mM). Although the data obtained do not clarify the molecular basis of H2O2 toxicity and/or do not explain the specific function of superoxide ions in H2O2-induced bacterial inactivation, they certainly demonstrate that the latter species plays a key role in both modes of H2O2 lethality. A mechanism of H2O2 toxicity in E. coli is proposed, involving the action of a hypothetical enzyme which should work as an O2-• generating system. This enzyme should be active at low concentrations of H2O2 (<5 mM) and high concentrations of the oxidant (>5 mM) should inactivate the same enzyme. Superoxide ions would then be produced and result in mode one lethality. The resistance at intermediate H2O2 concentrations may be dependent on the inactivation of such enzyme with no superoxide ions being produced at levels of H2O2 in the range 5–10 mM. Mode two killing could be produced by the hydroxyl radical in concert with superoxide ions, chemically produced via the reaction of high concentrations of H2O2 (>10 mM) with hydroxyl radicals. The rate of hydroxyl radical production may be increased by the higher availability of Fe2+ since superoxide ions may also reduce trivalent iron to the divalent form. 相似文献
12.
RuBPCO kinetics and the mechanism of CO2 entry in C3 plants 总被引:2,自引:1,他引:1
Abstract. The CO2 partial pressure in the chloroplasts of intact photosynthetic C3 leaves is thought to be less than the intercellular CO2 partial pressure. The intercellular CO2 partial pressure can be calculated from CO2 and H2O gas exchange measurements, whereas the CO2 partial pressure in the chloroplasts is unknown. The conductance of CO2 from the intercellular space to the chloroplast stroma and the CO2 partial pressure in the chloroplast stroma can be calculated if the properties of photosynthetic gas exchange are compared with the kinetics of the enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO). A discrepancy between gas exchange and RuBPCO kinetics can be attributed to a deviation of CO2 partial pressure in the chloroplast stroma from that calculated in the intercellular space. This paper is concerned with the following: estimation of the kinetic constants of RuBPCO and their comparison with the CO2 compensation concentration; their comparison with differential uptake of 14CO2 and 12CO2; and their comparison with O2 dependence of net CO2 uptake of photosynthetic leaves. Discrepancy between RuBPCO kinetics and gas exchange was found at a temperature of 12.5 °C, a photosynthetic photon flux density (PPFD) of 550 μmol quanta m?2 s?1, and an ambient CO2 partial pressure of 40 Pa. Consistency between RuBPCO kinetics and gas exchange was found if CO2 partial pressure was decreased, temperature incresed and PPFD decreased. The results suggest that a discrepancy between RuBPCO kinetics and gas exchange is due to a diffusion resistance for CO2 across the chloroplast envelope which decreases with increasing temperature. At low CO2 partial pressure, the diffusion resistance appears to be counterbalanced by active CO2 (or HCO3) transport with high affinity and low maximum velocity. At low PPFD, CO2 partial pressure in the chloroplast stroma appears to be in equilibrium with that in the intercellular space due to low CO2 flux. 相似文献
13.
L.J. Roberts B.J. Sweetman J.L. Morgan N.A. Payne J.A. Oates 《Prostaglandins & other lipid mediators》1977,13(4):631-647
Thromboxane B2 (TxB2) was biosynthesized from prostaglandin endoperoxides (PGG2, PGH2) using guinea pig lung microsomes and infused into an unanesthetized monkey. Urine was collected and TxB2 metabolites were isolated by reversed phase partition chromatography and high performance liquid chromatography. A major metabolite (TxB2-M) was found to be excreted in greater than two-fold abundance relative to other metabolites. Its structure was determined by gas chromatography-mass spectrometry to be dinorthromboxane B2. incubation of TxB2 with rat liver mitochondria yielded a C18 derivative with a mass spectrum identical to that of TxB2-M, substantiating that the major urinary metabolite of TxB2 in the monkey is a product of a single step of β-oxidation. 相似文献
14.
98.9% of 5092 flowers from 1041 individuals of Circaeaster agrestis have five floral organs, the formula is P3A1G1 (73.13%), P2A2G1 (25.59%), and P2A1G2 (0.22%). Only 0.4% of the flowers have six floral organs and the formula is P3A1G2 (20 flowers) or P3A2G1 (one flower). All these flowers have one vascular bundle in the pedicel and were considered to be normal ones. There are
33 flowers (0.65%) with six or more floral organs and two vascular bundles in the pedicel and we found traces of fusion of
different degree of two flowers into one. These flowers were considered as abnormal. Therefore the normal number of floral
organs of C. agrestis is five and occasionally six, and the floral formulas are P3A1G1 or P2A2G1, sometimes P2A1G2, and occasionally P3A1G2 or P3A2G1. A tepal in P3A1G1 may be replaced by a stamen in P2A2G1 or by a carpel in P2A1G2 or in reverse. A carpel in P3A1G2 may be replaced by a stamen in P3A2G1 or in reverse. We hypothesize that there are two possibilities for the number of the floral organs to be five (six), the
result of reduction from P3A2G2, or there exists homeosis among floral organs. 相似文献
15.
Titanium complexes with chiral amino alcohol ligands are useful precatalysts for the intramolecular hydroamination of aminoallenes. They can be synthesized via protonolysis of titanium dimethylamide starting materials with the free ligand. In most cases, the resulting materials are not isolable due to their oily nature. However, several complexes were prepared in pure form and isolated as solid materials. [Ti(Cl)(NMe2)(-OCH2CH(Ph)N(CHMe2)-]2 was prepared at room temperature from TiCl(NMe2)3 and the corresponding N-substituted d-amino alcohol; the dimeric nature of the complex was established by X-ray crystallography. [Ti(NMe2)2(-OCH2CH(Ph)N(2-Ad)-)]2 (2-Ad = 2-Adamantyl) was prepared from Ti(NMe2)4 and the corresponding N-substituted l-amino alcohol after prolonged heating. An intermediate complex that could not be purified or isolated is believed to be Ti(NMe2)3(-OCH2CH(Ph)NH(2-Ad)). Two complexes with the composition TiCl2(-OCH2CH(R*)N(CHMe2)-)(HNMe2) (where R* = CH2Ph or CHMe2) were prepared at room temperature by protonolysis of TiCl2(NMe2)2 with the corresponding N-substituted l-amino alcohols. These two complexes exhibit dynamic behavior on the NMR timescale that is believed to be a dimer-monomer equilibrium, but they decompose at elevated temperatures. 相似文献
16.
Although telemetered heart rate (fH) has been used as a physiological correlate to predict the metabolic rate (as oxygen consumption, V?O2) of fish in the field, it is our contention that the method has not been validated adequately for fish. If fH in fish is to be used to estimate V?O2, a single linear (or log-linear) relationship must be established for each species between the two variables which allows V?O2 to be predicted accurately under all environmentally relevant conditions. Our analyses of existing data indicate that while a good linear (or log-linear) relationship can be established between fH and V?O2, the conditions under which the relationship applies may be quite restricted. Physiological states and environmental factors affect the relationship between fH and V?O2 significantly such that several curves can exist for a single species. In addition, there are situations in which fH and V?O2 do not covary in a significant manner. In some situations fH can vary over much of its physiological range while V?O2 remains constant; in others V?O2 may vary while fH is invariate. The theoretical basis for this variability is examined to explain why the use of telemetered fH in predicting V?O2 of fish may be limited to certain specified applications. 相似文献
17.
《Bioorganic & medicinal chemistry》2014,22(20):5692-5696
An in situ H2O2 generation approach to promote P450 peroxygenases catalysis was developed through the use of the nicotinamide cofactor analogue 1-benzyl-1,4-dihydronicotinamide (BNAH) and flavin mononucleotide (FMN). Final productivity could be enhanced due to higher enzyme stability at low H2O2 concentrations. The H2O2 generation represented the rate-limiting step, however it could be easily controlled by varying both FMN and BNAH concentrations. Further characterization can result in an optimized ratio of FMN/BNAH/O2/biocatalyst enabling high reaction rates while minimizing H2O2-related inactivation of the enzyme. 相似文献
18.
Wastewater treatment plants are known to be important point sources for nitrous oxide (N2O) in the anthropogenic N cycle. Biofilm based treatment systems have gained increasing popularity in the treatment of wastewater, but the mechanisms and controls of N2O formation are not fully understood. Here, we review functional groups of microorganism involved in nitrogen (N) transformations during wastewater treatment, with emphasis on potential mechanism of N2O production in biofilms. Biofilms used in wastewater treatment typically harbour aerobic and anaerobic zones, mediating close interactions between different groups of N transforming organisms. Current models of mass transfer and biomass interactions in biofilms are discussed to illustrate the complex regulation of N2O production. Ammonia oxidizing bacteria (AOB) are the prime source for N2O in aerobic zones, while heterotrophic denitrifiers dominate N2O production in anoxic zones. Nitrosative stress ensuing from accumulation of NO2 ? during partial nitrification or denitrification seems to be one of the most critical factors for enhanced N2O formation. In AOB, N2O production is coupled to nitrifier denitrification triggered by nitrosative stress, low O2 tension or low pH. Chemical N2O production from AOB intermediates (NH2OH, HNO, NO) released during high NH3 turnover seems to be limited to surface-near AOB clusters, since diffusive mass transport resistance for O2 slows down NH3 oxidation rates in deeper biofilm layers. The proportion of N2O among gaseous intermediates (NO, N2O, N2) in heterotrophic denitrification increases when NO or nitrous acid (HNO2) accumulates because of increasing NO2 ?, or when transient oxygen intrusion impairs complete denitrification. Limited electron donor availability due to mass transport limitation of organic substrates into anoxic biofilm zones is another important factor supporting high N2O/N2 ratios in heterotrophic denitrifiers. Biofilms accommodating Anammox bacteria release less N2O, because Anammox bacteria have no known N2O producing metabolism and reduce NO2 ? to N2, thereby lowering nitrosative stress to AOB and heterotrophs. 相似文献
19.
Dimeric HER2-specific affibody molecules inhibit proliferation of the SKBR-3 breast cancer cell line
Ekerljung L Lindborg M Gedda L Frejd FY Carlsson J Lennartsson J 《Biochemical and biophysical research communications》2008,377(2):489-494
HER2-specific affibody molecules in different formats have previously been shown to be useful tumor targeting agents for radionuclide-based imaging and therapy applications, but their biological effect on tumor cells is not well known. In this study, two dimeric ((ZHER2:4)2 and (ZHER2:342)2) and one monomeric (ZHER2:342) HER2-specific affibody molecules are investigated with respect to biological activity. Both (ZHER2:4)2 and (ZHER2:342)2 were found to decrease the growth rate of SKBR-3 cells to the same extent as the antibody trastuzumab. When the substances were removed, the cells treated with the dimeric affibody molecules continued to be growth suppressed while the cells treated with trastuzumab immediately resumed normal proliferation. The effects of ZHER2:342 were minor on both proliferation and cell signaling. The dimeric (ZHER2:4)2 and (ZHER2:342)2 both reduced growth of SKBR-3 cells and may prove therapeutically useful either by themselves or as carriers of radionuclides or other cytotoxic agents. 相似文献
20.
The structures and stabilities of As2-doped Sin (n = 1-7) clusters have been investigated at the B3LYP level of theory, incorporating the 6-311+G∗ basis set. An isosceles triangle is predicted to be the lowest-energy structure of the As2Si cluster, whereas the global minimum of As2Si2 possesses an As-As-butterfly structure. The ground state structures for As2Si3, As2Si4 and As2Si5 are all bipyramids: trigonal, tetragonal and pentagonal, respectively, which could have important applications as building blocks to synthesize silicon nanowires. The most stable isomer of As2Si6 possesses a tricapped trigonal bipyramid structure. The lowest energy structure of As2Si7 can be viewed as a substitutional structure of the tricapped trigonal prism Si9 isomer. In the majority of the lowest energy isomers, the two As atoms tend to be separated from each other, in order to maximize the number of Si-As bonds, and therefore locate at the axial vertex or face-capping atomic positions, especially for As2Si4-As2Si7. According to results of the incremental binding energies, the HOMO-LUMO gaps and the vertical ionization potentials, the As2Si3 and As2Si6 clusters are relatively stable compared to their neighbors. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds play an important role in stabilizing the low-energy As2Sin structures. 相似文献