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1.
《BBA》1986,849(1):121-130
The binding of 3′-O-(1-naphthoyl)adenosinetriphosphate (1-naphthoyl-ATP), ATP and ADP to TF1 and to the isolated α and β subunits was investigated by measuring changes of intrinsic protein fluorescence and of fluorescence anisotropy of 1-naphthoyl-ATP upon binding. The following results were obtained. (1) The isolated α and β subunits bind 1 mol 1-naphthoyl-ATP with a dissociation constant (KD(1-naphthoyl-ATP)) of 4.6 μM and 1.9 μM, respectively. (2) The KD(ATP) for α and β subunits is 8 μM and 11 μM, respectively. (3) The KD(ADP) for α and β subunits is 38 μM μM and 7 μM, respectively. (4) TF1 binds 2 mol 1-naphthoyl-ATP per mol enzyme with KD = 170 nM. (5) The rate constant for 1-naphthoyl-ATP binding to α and β subunit is more than 5 · 104 M−1s−1. (6) The rate constant for 1-naphthoyl-ATP binding to TF1 is 6.6 · 103 M−1 · s−1 (monophasic reaction); the rate constant for its dissociation in the presence of ATP is biphasic with a fast first phase (kA−1 = 3 · 10−3s−1) and a slower second phase (kA−2 < 0.2 · 10−3s−1). From the appearance of a second peak in the fluorescence emission spectrum of 1-naphthoyl-ATP upon binding it is concluded that the binding sites in TF1 are located in an environment more hydrophobic than the binding sites on isolated α and β subunits. The differences in kinetic and thermodynamic parameters for ligand binding to isolated versus integrated α and β subunits, respectively, are explained by interactions between these subunits in the enzyme complex. 相似文献
2.
《生物化学与生物物理学报:生物膜》1986,862(1):199-204
The endocytotic rate constant, ke, originally described for the quantification growth factor by fibroblasts (Wiley, H.S. and Cunningham, D.D.(1982) J. Biol. Chem. 257, 4222–4229) has been adapted to measure receptor-mediated endocytosis of asialoglycoproteins by hepatocytes. A ke value of 0.21 min−1 was obtained for the internalisation of β-d-galactosyl bovine serum albumin by freshly isolated hepatocytes. The addition of ethaniol to the incubation medium had a biphasic effect on e. The value of ke was increased by up to 30% by low concentrations of ethanol, whereas higher concentrations progressively decreased ke and in 500 mM ethanol the ke value was 0.1 min−1. The amount of ligand bound to the cell surface was independent of the extracellular concentration of ethanol and the changes in ke were exclusively due to changes in the amount of internalised ligand. There was a progressive decrease in the value of ke in hepatocytes prepared from rats that were maintained on an ethanol-impregnated liquid diet for up to 20 days. The decrease was already apparent by day 2 when blood alcohol levels were only 50 mg%, indicating that the effects of chronic alcoholism on endocytosis are manifested at an early stage. 相似文献
3.
We examine the synchrony in the dynamics of localized [Ca2 + ]i oscillations among a group of cells exhibiting such complex Ca2 + oscillations, connected in the form of long chain, via diffusing coupling where cytosolic Ca2 + and inositol 1,4,5-triphosphate are coupling molecules. Based on our numerical results, we could able to identify three regimes, namely desynchronized, transition and synchronized regimes in the (T − ke) (time period-coupling constant) and (A − ke) (amplitude-coupling constant) spaces which are supported by phase plots (Δϕ verses time) and recurrence plots, respectively. We further show the increase of synchronization among the cells as the number of coupling molecules increases in the (T − ke) and (A − ke) spaces. 相似文献
4.
The yield of the triplet state of the primary electron donor of Photosystem I of photosynthesis (PT-700) and the characteristic parameters (g value, line shape, saturation behavior) of the ESR signal of the photoaccumulated intermediary acceptor A have been measured for two types of Photosystem I subchloroplast particles: Triton particles (TSF 1, about 100 chlorophyll molecules per P-700) that contain the iron-sulfur acceptors FX, FB and FA, and lithium dodecyl sulfate (LDS) particles (about 40 chlorophyll molecules per P-700) that lack these iron-sulfur acceptors. The results are: (i) In Triton particles the yield of PT-700 upon illumination is independent of the redox state of A and of FX,B,A and is maximally about 5% of the active reaction centers at 5 K. The molecular sublevel decay rates are kx = 1100 s?1 ± 10%, ky = 1300 s?1 ± 10% and kz = 83 s?1 ± 20%. In LDS particles the triplet yield decreases linearly with concentration of reduced intermediary acceptors, the maximal yield being about 4% at 5 K assuming full P-700 activity. (ii) In Triton particles the acceptor complex A consists of two acceptors A0 and A1, with A0 preceding A1. In LDS particles at temperatures below ?30°C only A0 is photoactive. (iii) The spin-polarized ESR signal found in the time-resolved ESR experiments with Triton particles is attributed to a polarized P-700-A?1 spectrum. The decay kinetics are complex and are influenced by transient nutation effects, even at low microwave power. It is concluded that the lifetime at 5 K of P-700A0A?1 must exceed 5 ms. We conclude that PT-700 originates from charge recombination of P-700A?0, and that in Triton particles A0 and A1 are both photoaccumulated upon cooling at low redox potential in the light. Since the state P-700AF?X does not give rise to triplet formation the 5% triplet yield in Triton particles is probably due to centers with damaged electron transport. 相似文献
5.
I.Kofi Adzamli Henry Ong Wah Kim A.Geoffrey Sykes George V. Buxton 《Journal of inorganic biochemistry》1982,16(4):311-317
The reaction of parsley 2Fe-2S ferredoxin in the normal oxidized state with eaq? generated by pulse radiolysis techniques has been studied at ~25°C, pH 7–8, I = 0.10 M (NaClO4). Rate constants ke (eaq? decay) and kp (protein absorbance change) are the same, second-order rate constant 9.7 × 109 M?1 sec?1. The reaction exhibits close to 100% efficiency. With 8Fe-8S ferredoxin from Clostridium pasteurianum under identical conditions it now appears that kp (although sometimes significantly smaller) is equal to ke. Varying efficiencies are also observed with this protein depending on the batch used. The reasons for such variable behavior are not fully understood. With oxidized and reduced forms of Chromatium v. high-potential iron-sulfur protein (HIPIP), ke and kp are essentially the same, but the highest efficiency observed is only ~50%. The prevailing pattern is therefore that rate constants ke and kp are generally in step for proteins having a single (or identical) active site(s). When the active site is buried as with HIPIP the efficiency of the reaction appears to decrease. 相似文献
6.
《农业工程》2014,34(6):342-350
The increased use of nitrogen fertilizers in agriculture would cause migration of nitrogen to surface and groundwater; accordingly, would lead to water resources contamination. The objective of this study is to investigate the effect of potassium zeolite on nitrate and ammonium ions sorption and retention in a saturated sandy loam soil in a laboratory condition. The study was conducted as a completely randomized block design with four treatments of 0, 2, 4 and 8 g zeolite per kilogram soil and three replications. Ammonium nitrate fertilizer with concentration of 10 g l−1 was added to soil columns and then leaching was performed. The results show that increasing potassium zeolite to soil causes reduction to the mobility of both nitrate and ammonium and enhancement of the retention of ions in soil. Ions leaching were simulated with convection–dispersion-equation (CDE) and mobile–immobile model (MIM) using HYDRUS-1D code. The results indicate that ammonium ion sorption by soil followed the Freundlich isotherm model. Absorption isotherms and dispersion (De) coefficient were determined through the inverse modeling for both ions. Based on the results, optimized values of Freundlich isotherm were much less than the observed amounts. This shows that the HYDRUS-1D model underestimated the adsorption parameters to predict the ammonium ion mobility in soil macropores. Since soil has been disturbed, the prediction of CDE model was equal to MIM model approximately. Both models showed that as the amount of applied zeolite increases, the dispersion (De) coefficient of nitrate and ammonium ions in the soil increases. 相似文献
7.
《Inorganica chimica acta》1988,152(2):91-99
The reactions of PtCl2en or cis-Pt(NH3)2Cl2 and their aqua species with adenine and adenosine were studied by means of ion-pair HPLC. From the chromatograms, it was found that the first binding site of Pt(II) was the N(7) site of adenine under both acidic and neutral conditions. The rates of Pt(II) binding at the (N7) site of adenosine and deoxyadenosine were measured. The rate constants, k1, were obtained for the reactions of PtCl2en or cis-Pt(NH3)2Cl2 with adenosine and deoxyadenosine at pH 3 and 7 over the temperature range 9–25 °C. The k1 values were 6.8–7.7 × 10−4 dm3 mol−1 s−1 at 25 °C. For the aqua species, the rate of [cis-Pt(NH3)2ClH2O]+ with adenosine N(7) was measured. The rate constants, k2 which were found to be smaller than those of hydrolysis, kh, were calculated at pH 3 over the temperature range 25–40 °C. The k2 value obtained at 25 °C was 1.1 × 10−2 dm3 mol−1 s−1, 15 time larger than k1. The activation parameters were also calculated. 相似文献
8.
《Bioorganic & medicinal chemistry》2014,22(21):5838-5846
A novel scaffold derived from l-SPD with a substituted thiophene group in the D ring were designed, synthesized, and evaluated for their binding affinities at dopamine (D1, D2 and D3) and serotonin (5-HT1A and 5-HT2A) receptors. Most of the tetracyclic compounds exhibited higher affinities for D2 and 5-HT1A receptors than l-SPD, while compound 23e showed the highest Ki value of 7.54 nM at D2 receptor which was 14 times more potent than l-SPD. Additionally, compounds 23d and 23e were more potent than l-SPD at D3 receptor. According to the functional assays, 23d and 23e were demonstrated as full antagonists at D1 and D2 receptors and full agonists at 5-HT1A receptor. Since the combination of D2 antagonism and 5-HT1A agonism is considered effective in treating both the positive and negative symptoms of schizophrenia, these novel compounds are implicated as potential therapeutic agents. 相似文献
9.
《Inorganica chimica acta》1987,128(1):87-92
The kinetics of malonate replacement in bis- (malonato)oxovanadate(IV), [VO(mal)2H2O]2−(hereafter water molecule will be omitted), by oxalate has been studied by the stopped-flow method. The reaction was found to consist of two consecutive steps (k1 and k2: first-order rate constants) passing through a mixed ligand complex, [VO(mal)(ox)]2−. The rates for each step depended linearly on the concentrations of free oxalate species, Hox− and ox2−. The second-order rate constants for the replacement by ox2− were much larger in the k1 step than in the k2 step and the activation parameters were determined as follows: ΔH≠= 43.5 ± 5.6 kJ mol−1, ΔS±-53 ± 19 J K−1 mol−1 and ΔH≠= 43.6 ± 0.5 kJ mol−1, δS≠ = -62 ± 2 J K−l mol−1 for the k1 and k2 steps, respectively. The volume of activation was determined to be -0.65 ± 0.75 cm3 mol−1 at 20.2 °C by the high-pressure stopped-flow method for the apparent rate constants. 相似文献
10.
Background and aims
Elevated atmospheric CO2 (eCO2) and tropospheric O3 (eO3) can alter soil microbial processes, including those underlying N2O emissions, as an indirect result of changes in plant inputs. In this study, effects of eCO2 and eO3 on sources of N2O in a soybean (Glycine max (L.) Merr.) agroecosystem in Illinois (SoyFACE) were investigated. We hypothesized that increases in available C and anaerobic microhabitat under eCO2 would stimulate N2O emissions, with a proportionally larger increase in denitrification derived N2O (N2OD) compared to nitrification plus nitrifier denitrification derived N2O (N2ON+ND). We expected opposite effects under eO3.Methods
Isotopically labeled 15NH 4 14 NO3 and 14NH 4 15 NO3 were used to evaluate mineral N transformations, N2OD, and N2ON+ND in a 12-day incubation experiment.Results
We observed minimal effects of eCO2 and eO3 on N2O emissions, movement of 15?N through mineral N pools, soil moisture content and C availability. Possibly, altered C and N inputs by eCO2 and eO3 were small relative to the high soil organic C content and N-inputs via biological N2-fixation, minimizing potential effects of eCO2 and eO3 on N-cycling.Conclusion
We conclude that eCO2 and eO3 did not affect N2O emissions in the short term. However, it remains to be tested whether N2O emissions in SoyFACE will be unaltered by eCO2 and eO3 on a larger temporal scale under field conditions. 相似文献11.
The electron-transfer reactions and thermodynamic equilibria involving the quinone acceptor complex in bacterial reaction centers from R. sphaeroides were investigated. The reactions are described by the scheme: We found that the charge recombination pathway of D+QAQ?B proceeds via the intermediate state D+Q?AQB, the direct pathway contributing less than approx. 5% to the observed recombination rate. The method used to obtain this result was based on a comparison of the kinetics predicted for the indirect pathway (given by the product kAD-times the fraction of reaction centers in the Q?AQB state) with the observed recombination rate, kobsD+ →D. The kinetic measurements were used to obtain the pH dependence (6.1 ? pH ? 11.7) of the free energy difference between the states Q?AQB and QAQ?B. At low pH (less than 9) QAQ?B is stabilized relative to Q?AQB by 67 meV, whereas at high pH Q?AQB is energetically favored. Both Q?A and Q?B associate with a proton, with pK values of 9.8 and 11.3, respectively. The stronger interaction of the proton with Q?B provides the driving force for the forward electron transfer. 相似文献
12.
In normalyears, eggs and prolarvae of the plaice (Pleuronectes platessa L.) in the southern North Sea develop within the temperature range 6.0–8.5 °C, although the water may at times be some degrees colder or warmer than this. The effect of temperature, t °C, on the embryonic development time, D days, has been investigated within the tolerated range 2.8–10.5 °C. Various models to express the observed curvilinear relationship between t and D have been considered, that giving the closest fit to the data being (t−t0)(D−D0) = k or . A method is given for the calculation of constants k, D0, and t0. The relationship may also be expressed by the equation D = a(t−t0)b where a and b are constants, but t0 must in this case be found by iteration. At investigated temperatures in the range 4.1–10.5 °C the smallest eggs in a batch from a single source hatched first. Within the tolerated range, hatching prolarvae were substantially smaller at 10.5 °C than at the other temperatures. During the period of prolarval yolk utilization, growth is slower at the high temperatures, so that median temperatures of 6.5–8.0 °C are most efficient in terms of the relationship between growth in length and yolk utilization. Toward the end of the yolk-sac phase, the rate of yolk utilization declines unless a suitable external food source (e.g., Artemia nauplii) is provided. 相似文献
13.
《BBA》1987,891(3):286-292
Photosystem I charge separation in a subchloroplast particle isolated from spinach was investigated by electron spin resonance (ESR) spectroscopy following graduated inactivation of the bound iron-sulfur centers by urea-ferricyanide treatment. Previous work demonstrated a differential decrease in iron-sulfur centers A, B and X which indicated that center X serves as a branch point for parallel electron flow through centers A and B (Golbeck, J.H. and Warden, J.T. (1982) Biochim. Biophys. Acta 681, 77–84). We now show that during inactivation the disappearance of iron-sulfur centers A, B, and X correlates with the appearance of a spin-polarized triplet ESR signal with |D| = 279·10−4 cm−1 and |E| = 39·10−4 cm−1. The triplet resonances titrate with a midpoint potential of +380 ± 10 mV. Illumination of the inactivated particles results in the generation of an asymmetric ESR signal with g = 2.0031 and ΔHpp = 1.0 mT. Deconvolution of the P-700+ contribution to this composite resonance reveals the spectrum of the putative primary acceptor species, A0, which is characterized by g = 2.0033 ± 0.0004 and ΔHpp = 1.0 ± 0.2 mT. The data presented in this report do not substantiate the participation of the electron acceptor A1 in PS I electron transport, following destruction of the iron-sulfur cluster corresponding to center X. We suggest that A1 is closely associated with center X and that this component is decoupled from the electron-transport path upon destruction of center X. The inability to photoreduce A1 in reaction centers lacking a functional center X may result from alteration of the reaction center tertiary structure by the urea-ferricyanide treatment or from displacement of A1 from its binding site. 相似文献
14.
《Aquatic Botany》2007,86(2):107-116
The partitioning of latent heat flux (QE) to vascular plant and moss surface components was assessed for a Sphagnum-dominated bog with a hummock–hollow surface having a sparse canopy of low shrubs. Results from porometry and eddy covariance measurements of QE showed evaporation from the moss surface ranged from greater than 50% of total QE early in the growing season to less than 20% after a dry period toward the end of the growing season. Both soil moisture and vapour pressure deficit (Da) affected this partitioning with drier moss and peat, lower water table, and smaller Da all reducing moss QE. Daily maximum moss QE ranged from greater than 200 W m−2 early in the growing season to less than 100 W m−2 during a dry period. In contrast, vascular contribution to total QE increased over the season from a daily maximum of about 150 W m−2 to 250 W m−2 due to increase in leaf area by leaf replacement and emergence and to drying of the moss surface. Porometry results showed average daily maximum conductance from bog shrubs was near 8 mm s−1. These conductance values were smaller than those reported for vascular plants from more nutrient-rich wetlands. The effect of increases in Da on vascular QE were moderated by decreases in stomatal conductance. At constant available energy, vascular leaf conductance was reduced by as much as 2 mm s−1 and moss surface conductance was enhanced by up to 3 mm s−1 by large Da. Considering vascular and non-vascular water transport characteristics and frequency of water table position and given the observed variations of QE partitioning with water table location and moss and peat water content, it is suggested that modelling efforts focus on how dry hummocks and wet hollows each contribute to QE, especially as related to Da and soil moisture dynamics. 相似文献
15.
《Inorganica chimica acta》1987,138(1):61-65
The kinetics and mechanism of a linear trihydroxamic acid siderophore (deferriferrioxamine B, H4DFB+) ligand exchange with Al(H2O)63+ to form mono(deferriferrioxamine B)aluminum(III) (Al(H2O)4H3DFB)3+ have been investigated at 25 °C over the [H+] range 0.001−1.0 M and I = 2.0 M (HClO4/NaClO4) by 27Al NMR. Kinetic results are consistent with Al(H2O)4(H3DFB)3+ formation and dissociation proceeding through a parallel path mechanistic scheme involving Al(H2O)63+(k2/k−1) and Al(H2O)5(OH)2+(k2/k−2) where k1 = 0.13 M−1 s−1, k−1 = 8.7 × 10−3 M−1 s−1, k2 = 2.7 × 103 M−1 s−1, and k−2 = 9.6 × 10−4 s−1. Relative complex formation rates at Al(H2O)63+ and Al(H2O)5OH2+, and comparison with kinetic data for a series of synthetic hydroxamic acids, suggest that an interchange mechanism is operative. These results are also discussed in relation to kinetic data for the corresponding iron(III)-deferriferrioxamine B system. 相似文献
16.
《BBA》2006,1757(9-10):1133-1143
In cytochrome c oxidase, oxido-reductions of heme a/CuA and heme a3/CuB are cooperatively linked to proton transfer at acid/base groups in the enzyme. H+/e− cooperative linkage at Fea3/CuB is envisaged to be involved in proton pump mechanisms confined to the binuclear center. Models have also been proposed which involve a role in proton pumping of cooperative H+/e− linkage at heme a (and CuA). Observations will be presented on: (i) proton consumption in the reduction of molecular oxygen to H2O in soluble bovine heart cytochrome c oxidase; (ii) proton release/uptake associated with anaerobic oxidation/reduction of heme a/CuA and heme a3/CuB in the soluble oxidase; (iii) H+ release in the external phase (i.e. H+ pumping) associated with the oxidative (R → O transition), reductive (O → R transition) and a full catalytic cycle (R → O → R transition) of membrane-reconstituted cytochrome c oxidase. A model is presented in which cooperative H+/e− linkage at heme a/CuA and heme a3/CuB with acid/base clusters, C1 and C2 respectively, and protonmotive steps of the reduction of O2 to water are involved in proton pumping. 相似文献
17.
《Comparative biochemistry and physiology. C: Comparative pharmacology》1992,101(3):495-498
1. [3H]Saxitoxin, a sodium channel probe, was found to bind reversibly with high affinity to a single class of noninteracting sites in membrane preparations from whole head homogenates of tobacco budworm, Heliothis virescens (F.), moths from a pyrethroid susceptible strain and from a pyrethroid resistant strain with nerve insensitivity and metabolic resistance mechanisms.2. No significant interstrain differences were detected in saturation (KD, Bmax) and kinetic (k+1, k−1) experiments.3. Also, five pyrethroids, two formamidines, and DDT had no significant effect on [3H]saxitoxin binding when tested at concentrations of 1 × 10−4 and 1 × 10−8 M.4. It appeared that a decreased density in sodium channels in resistant strain moths as compared with that in susceptible strain moths was not a factor in pyrethroid-induced resistance in this particular strain of tobacco budworm. 相似文献
18.
《Inorganica chimica acta》1988,150(1):81-100
The (NH3)5CoOC(NH2)23+ ion is consumed in water according to the rate law k(obs.) = k1 + k2[OH−], where k1 = 4.0 × 10−5 s−1 and k2 = 14.2 M−1 s−1 (0–0.1 M [OH−];μ = 1.1 M, NaClO4, 25 °C). A hitherto unrecognized intramolecular O- to N- linkage isomerization reaction has been detected. In strongly acid solution only aquation to (NH3)5CoOH23+ is observed, but in 0.1–1.0 M [OH−], 7% of the directly formed products is the urea-N complex (NH3)5CoNHCONH22+ which has been isolated. In the neutral pH region a much greater proportion (25%) of the products is the urea-N species. These results are interpreted in terms of an urea-O to urea-N linkage isomerization reaction competing with hydrolysis for both spontaneous (k1) and base-catalyzed (k2) pathways; the rearrangement is not observed in strongly acidic solution (pH ⩽ 1) because the protonated N-bonded isomer (pK′a ≈ 3) is unstable with respect to the O-bonded form. The appearance of the isomerization pathway as the pH is raised in the 0–6 region is commensurate with a rate increase which cannot be attributed to a contribution from the base catalysis term k2[OH−]. It is argued that this observation establishes, for the spontaneous pathway, that hydrolysis and linkage isomerization are separate reaction pathways — there is no common intermediate. The product distribution and rate data lead to the complete rate law, k(obs.) = k1 + k2[OH−] = (ks + kON) + (kOH + k′ON) [OH−] for the reactions of the O-bonded isomers, where ks, kOH are the specific rates for hydrolysis, and kON, k′ON are the specific rates for O- to N-linkage isomerization, by spontaneous and base-catalyzed pathways respectively; kON = 1.3 × 10−5 s−1 and k′ON = 1.1 M−1 s−1 (μ = 1.0 M, NaClO4, 25 °C). The O- to N- linkage isomerization has been observed also for complexes of N-methylurea, N,N-dimethylurea and N-phenylurea, but not for the N,N′-dimethylurea species. There is an approximately statistical relationship among the data for −NH2 capture (versus H2O), while −NHR and −NR2 do not compete with water as nucleophiles for Co(III) in either the spontaneous or base-catalyzed hydrolysis processes. For each urea-O complex, O- to N-isomerization is a more significant parallel reaction in the spontaneous as opposed to the base-catalyzed pathway. This is interpreted as being indicative of more associative character in the spontaneous route to products, a conclusion supported by other evidence. Some activation parameter data have been recorded and the effect of the N-substitution on the rates of solvolysis (H2O, Me2SO) is discussed. The urea-N complexes have been isolated as their deprotonated forms, [(NH3)5CoNHCONRR′](ClO4)2·xH2O (R,R′ = H, CH3). They are kinetically inert in neutral to basic solution but in acid they protonate (H2O, pK′a 2–3; μ = 1.0 M, 25 °C) and then isomerize rapidly back to their O-bonded forms. Some solvolysis accompanies this N- to O-rearrangement in H2O and Me2SO. Specific rates and activation parameters are reported. The kinetic data follow a rate law of the form kNO(obs.) = (k + kNO)[H+]/(K′a + [H+]) and the active species in the reaction is the protonated form; k, kNO are the specific rates for hydrolysis and isomerization, respectively. Proton NMR data establish that the site of protonation (in Me2SO) is the cobalt-bound nitrogen atom. For the unsubstituted urea species (NH3)5CoNH2CONH23+, diastereotopic exo-NH2 protons arising from restricted rotation about the CN bond are observed. The relevance to the mechanism of the linkage isomerization process is considered. 13C and 1H NMR and electronic absorption spectral data are presented, and distinctions between linkage isomers and the solution structures (electronic and conformational) are discussed. The urea-N/urea-O complex equilibrium is governed by the relation K′NO(obs.) = K′NO[H+]/[H+](K′a), where K′NO is the equilibrium constant = [(NH35Co(urea-O)3+]/[(NH3)5Co(urea-N)3+]. Values for K′NO(=kNO/kON = 260 and pK′a ≈ 3 for the NH2CONH2 system are consistent with the stability of the N-isomer in feebly acidic to basic solution (e.g. pH 6, K′NO(obs.) = 2.6 × 10−2) and instability in acid solution (e.g. pH 1, K′NO(obs.) = 240). The equilibrium data for this and other urea complexes of (NH3)5Co(III) are contrasted with the result for the analogous Rh(III)NH2CONH2 system K′NO ≈ 1). 相似文献
19.
《Journal of Fermentation and Bioengineering》1990,69(4):215-219
Factors affecting the rates of plasmid transfer were investigated using Escherichia coli LC102 bearing a conjugative plasmid R100-1 and E. coli DH1. The rate constant of transconjugant increase, kti, was used for presenting the degree of plasmid transmissibility instead of the plasmid transfer efficiency (pte). The rate constant was defined as the specific rate of transconjugant increase (srti, the number of transconjugants per donor per h) divided by the recipient cell concentration. The kti values ranged between 10−10 and 10−15 ml cells−1 h−1, when estimated under various conditions. Moderate liquid agitation had a favorable effect on ktf but agitation rates higher than 33 s−1 (intergrated shear force) greatly decreased the value of kti. The transconjugant-forming activity of the cells growing in continuous culture did not significantly change with the dilution rate, except those growing at dilution rates less than 0.1 h−1. The rate constant kti at temperatures of 10–15°C was as low as the detection limit (10−15 ml cells−1 h−1). 相似文献
20.
Haifeng Sun Liyuan Zhu Huicui Yang Wangke Qian Lin Guo Shengbin Zhou Bo Gao Zeng Li Yu Zhou Hualiang Jiang Kaixian Chen Xuechu Zhen Hong Liu 《Bioorganic & medicinal chemistry》2013,21(4):856-868
An effective and rapid method for the microwave-assisted preparation of the key intermediate for the total synthesis of tetrahydroprotoberberines (THPBs) including l-stepholidine (l-SPD) was developed. Thirty-one THPB derivatives with diverse substituents on A and D ring were synthesized, and their binding affinity to dopamine D1, D2 and serotonin 5-HT1A and 5-HT2A receptors were determined. Compounds 18k and 18m were identified as partial agonists at the D1 receptor with Ki values of 50 and 6.3 nM, while both compounds act as D2 receptor antagonists (Ki = 305 and 145 nM, respectively) and 5-HT1A receptor full agonists (Ki = 149 and 908 nM, respectively). These two THPBs compounds exerted antipsychotic actions in animal models. Further electrophysiological studies employing single-unit recording in intact animals demonstrated that 18k-excited dopaminergic (DA) neurons are associated with its 5-HT1A receptor agonistic activity. These results suggest that these two compounds targeted to multiple neurotransmitter receptors may present novel lead drugs with new pharmacological profiles for the treatment of schizophrenia. 相似文献