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1.
《Inorganica chimica acta》1988,145(2):303-308
The luminescence of the following ions in ScBO3 is reported: Ce3+, Gd3+, Eu3+ and Cr3+. The lanthanide ions show luminescence spectra which reveal the influence of the fact that these ions occupy a small site (Sc3+). The vibronic lines are relatively strong. The 4f → 5d bands are characterized by small Stokes shifts. The Cr3+ ion, however, shows the influence of occupying a large site: the crystal field is weak and the emission is of the broad-band type (4T2 → 4A2). The vibrational structure in this band is analyzed. 相似文献
2.
The signal events of 1 mM Ce4+ (Ce(NH4)2(NO3)6)-induced apoptosis of cultured Taxus cuspidata cells were investigated. The percentage of apoptotic cells increased from 0.82% to 51.32% within 6 days. Caspase-3-like protease activity became notable during the second day of Ce4+-treatment, and the maximum activity was 5-fold higher than that of control cells at the fourth day. When the experiment system was pretreated with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) at 100 M, caspase-3-like activity resulted in distinct inhibition by 70% and 77.3% after 3 and 4 days of induction. Furthermore, 100 M Ac-DEVD-CHO partially reduced the apoptotic cells by 58.6% and 60.8% at day 4 and 5 respectively. Ce4+ induced superoxide anions (O2·–) transient burst, and the first peak appeared at around 3.7–4 h, the second appeared at about 7 h. Both O2·– burst and cell apoptosis were effectively suppressed by application of diphenyl iodonium (NADPH oxidase inhibitor). Inhibition of O2·– production attenuated caspase-3-like activation by 49% and 53.6% during day 3 and 4 respectively. In addition, a total of 15 protein spots changed in response to caspase-3-like protease activation were identified by two-dimensional gel electrophoresis. These results suggest that Ce4+ of 1 mM induces apoptosis in suspension cultures of T. cuspidata through O2·– burst as well as caspase-3-like protease activation. The burst of O2·– exerts its activity as an upstream of caspase-3-like activation. Our results also implicate that other signal pathways independent of an O2·– burst possibly participate in mediating caspase-3-like protease activation. 相似文献
3.
The interactions between Hg2+, Ce3+, and the mixuure of Ce3+ and Hg2+, and DNA from fish intestine in vitro were investigated by using absorption spectrum and fluorescence emission spectrum.
The ultraviolet absorption spectra indicated that the addition of Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ to DNA generated an obviously hypochromic effect. Meanwhile, the peak of DNA at 205.2 nm blue-shifted and at 258.2 nm red-shifted.
The size of the hypochromic effect and the peak shift of DNA by metal ion treatments was Hg2+>Hg2++Ce3+>Ce3+. The fluorescence emission spectra showed that with the addition of Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ the emission peak at about 416.2 nm of DNA did not obviously change, but the intensity reduced gradually and the sequence
was Hg2+>Hg2++Ce2+>Ce3+. Hg2+, Ce3+, and the mixture of Ce3+ and Hg2+ had 1.12, 0.19, and 0.41 binding sites to DNA, respectively; the fluorescence quenching of DNA caused by the metal ions all
attributed to static quenching. The binding constants (K
A
) of binding siees were 8.98×104 L/mol and 1.02×104 L/mol, 5.12×104 L/mol and 1.10×103 L/mol, 6.66×104 L/mol and 2.36×103 L/mol, respectively. The results showed that Ce3+ could relieve the destruction of Hg2+ on the DNA structure. 相似文献
4.
Wenhui Zhang Hongqiu Zhao Ian Carmichael Anthony S. Serianni 《Carbohydrate research》2009,344(12):1582-9509
Methyl α-cellobioside (methyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranoside) was labeled with 13C at C4′ for use in NMR studies in DMSO-d6 solvent to attempt the detection of a trans-H-bond J-coupling (3hJCCOH) between C4′ and OH3. Analysis of the OH3 signal at 600 MHz revealed only the presence of two homonuclear J-couplings: 3JH3,OH3 and a smaller, longer range JHH. No evidence for 3hJC4′,OH3 was found. The longer range JHH was traced to 4JH4,OH3 based on 2D 1H–1H COSY data and inspection of the H2 and H4 signal lineshapes. A limited set of DFT calculations was performed on a methyl cellobioside mimic to evaluate the structural dependencies of 4JH2,O3H and 4JH4,O3H on the H3–C3–O3–H torsion angle. Computed couplings range from about −0.7 to about +1.1 Hz, with maximal values observed when the C–H and O–H bonds are roughly diaxial. 相似文献
5.
Ce3+‐doped orthosilicate oxyapatite NaY9(SiO4)6O2 phosphors NaY9–x(SiO4)6O2:xCe3+ were prepared by a conventional high‐temperature solid‐state reaction method, and their spectroscopic characteristics were systematically investigated. The occupancies of Ce3+ ions at two different sites (Wyckoff 6 h and 4f sites) in NaY9(SiO4)6O2 were determined. The influence of doping concentration on the emission intensity of Ce3+ was investigated and the critical distance Rc was estimated in terms of the concentration quenching data. 相似文献
6.
Cartuyvels E Van Hecke K Van Meervelt L Görller-Walrand C Parac-Vogt TN 《Journal of inorganic biochemistry》2008,102(8):1589-1598
The reaction of molybdate and dl-proline at pH 3.4 results in the formation of a Na4[Mo8O26(proO)2] · 22H2O complex (pro = proline) in which two proline ligands are attached to molybdenum(VI) ions via monodentate coordination of the carboxylate groups. The structure of the complex was determined by single crystal X-ray diffraction and by combination of 1H, 13C and 95Mo NMR spectroscopy techniques in solution. The structure of the complex is strongly dependant on the pH. At native pH 3.4 the octamolybdate-type structure seems to be present in solution, but the increase of pH to 5.8 resulted in a rearrangement of the structure to a heptamolybdate-type structure. At physiological pH, the polyoxometalate framework was completely dissociated into the monomeric unit. The reactivity of the Na4[Mo8O26(proO)2] · 22H2O towards the hydrolysis of ATP was tested at different pH values. While in solution at pH 3.4 the hydrolysis proceeded to yield AMP (adenosine monophosphate) and ADP (adenosine diphosphate) in nearly equal amounts, reaction mixture at pH 5.8 gave ADP as the only product of hydrolysis after 24 h of reaction. At neutral pH, the hydrolysis of ATP was slower, but it proceeded to yield 75% of ADP after 48 h of reaction. 相似文献
7.
Application of soil slurry respirometry to optimise and subsequently monitor ex situ bioremediation of hydrocarbon-contaminated soils 总被引:1,自引:0,他引:1
T.J. Aspray D.J.C. Carvalho J.C. Philp 《International biodeterioration & biodegradation》2007,60(4):279-284
A protocol to monitor respiration as O2 consumption in soil slurries using the Strathtox® respirometer was developed and tested on four soils from brownfield sites. Respiration rates (mg l−1 h−1) of soil slurries in the Strathtox® were compared with rates (μl min−1) of field moist soils analysed using the Columbus Oxymax® ER10 respirometer. One of the soils (99612B), historically contaminated with diesel, was further studied by monitoring the effect of inorganic NH4NO3 liquid nutrient on enhancing respiration rate. Soil microcosms were monitored continuously on the Oxymax® or sampled at 24, 48 and 72 h intervals, prepared as soil slurries, and analysed on the Strathtox®. On the full-scale remediation project (6000 m3) soil 99612B was treated as a biopile with spent mushroom compost (SMC) amendment and respiration rates monitored in samples over an 8-week period. In the laboratory microcosm experiment and full-scale bioremediation treatment described, correlation was found for respiration rates between the two respirometry systems. 相似文献
8.
Ying Wu 《Biometals》2000,13(3):195-201
The influences of mono-, bi- and trivalent metal ions (as chloride salts) on the activity of dihydrofolate reductase (DHFR) from chicken liver have been studied to elucidate the mechanism of ion-activation of this enzyme. The results show that monovalent ions (Na+ and K+) activate DHFR at low concentration reaching a maximum activation of about 2.5 fold at 0.4–0.5 M and declining at higher concentrations. Ca2+ shows similar activation but at lower concentration, reaching a maximum at 0.1 M; activity declines with further increases in concentration. At very high concentration (>0.4 M), Ca2+ is inhibitory. The trivalent lanthanide ions, however, show a dramatic inhibition of activity of DHFR even at very low concentration. The activity of DHFR declines to 50% of that of the control at 0.02 mM EuCl3. Intrinsic fluorescence measurements show that the ion-dependent activation in the presence of mono- and bivalent metal ions is due to the conformational changes in the protein. Energy transfer phenomenon suggests that the specific interaction of Eu3+ with Trp24 located in a loop at the active site of DHFR is responsible for the strong inhibition. The possible mechanism for the ion-inhibition is proposed and discussed. 相似文献
9.
Hitoshi Katada Hidetake Seino Yasushi Mizobe Jun Sumaoka Makoto Komiyama 《Journal of biological inorganic chemistry》2008,13(2):249-255
The structures of Ce4+ complexes that are active for DNA hydrolysis were determined for the first time by X-ray crystallography. The crystals were
prepared from a 1:2 mixture of Ce(NH4)2(NO3)6 and dipicolinic acid (2,6-pyridinedicarboxylic acid). Depending on the recrystallization conditions, three types of crystals
were obtained. Some of the Ce4+ ions in these complexes have enough coordinated water molecules that can directly and indirectly participate in the catalysis.
The distances between the Ce4+ and the dipicolinate ligand are considerably shorter than those in the corresponding La3+ and Ce3+ complexes. On the other hand, the distances between the Ce4+ and its coordinated water are similar to those for the La3+ and Ce3+ complexes. In a proposed mechanism of DNA hydrolysis, the scissile phosphodiester linkage is notably activated by coordination
to Ce4+ and attacked by the Ce4+-bound hydroxide. The process is further assisted by acid catalysis of Ce4+-bound water.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Three new lanthanide thiostannates [Ln2(en)6(μ2-OH)2]Sn2S6 (Ln = Nd (1), Gd (2); en = ethylenediamine) and [Gd(dien)3]2[(Sn2S6)Cl2] (3) (dien = diethylenetriamine) were first synthesized by treating LnCl3 with SnCl4 and S under mild solvothermal conditions. Compounds 1 and 2 are isostructural. They consist of a binuclear lanthanide(III) complex [Ln2(en)6(μ2-OH)2]4+ cation and a dimeric [Sn2S6]4− anion. The anion is built up by two SnS4 tetrahedra sharing a common edge. The Nd3+ and Gd3+ ions are in an eight-coordinated environment forming distorted bicapped trigonal prisms. Compound 3 is composed of two monouclear [Gd(dien)3]3+ complex cations, a [Sn2S6]4− anion, and two chlorine ions. The Gd3+ ion has a nine-coordinated environment forming a distorted tricapped trigonal prism. In compounds 1-3, extensive hydrogen bonds are formed leading to three-dimensional networks of anions and cations. The band gaps of 2.42 eV for 1 and 3.17 eV for 2 have been derived from optical absorption spectra. The new lanthanide compounds might be the precursors for ternary lanthanide thiostannates by the heat treatment under nitrogen atmosphere to get rid of organic components. 相似文献
11.
Five isostructural compounds of lanthanide with isonicotinate ligand, formula as [Ln(IN)2(H2O)4](NO3) (Ln = La, Nd, Eu, Tb and Er, 1−5, IN = isonicotinate), were synthesized under hydrothermal conditions by tuning the pH level and the ratio of lanthanide with isonicotinic acid. These compounds were characterized by single-crystal X-ray structure analysis, elemental analysis, IR and TG-DTA. In five compounds, the adjacent eight-coordination lanthanide centers were linked together through the bidentate bridging carboxylate groups of isonicotinate ligands to generate infinite chain structures which were further interconnected to form 3D supramolecular networks via the OW-H···N (nitrogen atom came from isonicotinate ligands) and OW-H···O (oxygen atom came from nitrate) hydrogen bonds. Compounds 3 and 4 show strong red and green emission, corresponds to 5D0→7F2 transition of Eu3+ ions and 5D4→7F5 transition of Tb3+ ions, respectively. 相似文献
12.
The binary complexation of Am3+, Cm3+and Eu3+ with citrate has been studied at I = 6.60 m (NaClO4), pcH 3.60 and in the temperatures range of 0-60 °C employing a solvent extraction technique with di-(2-ethylhexyl)phosphoric acid/heptane. Two complexes, MCit and , were formed at all temperatures. For the three metal ions, the log β101 was between 5.9 and 6.2 and log β102 between 10.2 and 10.6 at 25 °C. The thermodynamic parameters for the Am-Cit system have been calculated from the temperature dependence of the β101 and β102 values. Positive enthalpy and entropy values for the formation of both complexes are interpreted as due to the contributions from the dehydration of the metal ions exceeding the exothermic cation-anion pairing. The formation of the ternary complex M(EDTA)(Cit)4− (M = Cm and Eu) was measured to have large stability constants (log β111 between 20.9 and 24.4) at 25 and 60 °C. Time resolved laser luminescence spectroscopy and lifetime measurement data validated the nature of the complexes of Eu(III) formed in the presence of Cit and EDTA + Cit in 6.60 m (NaClO4) solution. 相似文献
13.
Physical and chemical conditions, particulate matter and N-uptake were characterized at two sampling sites at the eastern German coast of the Baltic Sea (Pomeranian Bay) over the annual period of 1997 (February–November). The inshore sampling sites (5 m water depth) differed with respect to the potential influences of river run-off and salt water exchange (mean values of salinity: 7.05 and 8.72 PSU), respectively. The mean org-Cdiss/org-Cpart-ratios (4.9 and 12.6) fell in the same order of magnitude (1.0–12.6) as values of neighboring inshore waters, and increasing values reflect an enhancement of the trophic level. Beside differences of nitrogen concentrations (dissolved inorganic nitrogen: 1.8–23.8 and 0.9–9.9 mol l–1), particulate nitrogen (4.30–41.01 and 2.69–9.08 mol l–1) and absolute uptake of N-nutrients (mean sum of NH4
+, urea, NO3
– uptake rates: 0.141 and 0.087 mol l–1 h–1), specific uptake of 15N-labelled nutrients (NH4
+, urea, NO3
–) as well as the relationships between the measured variables characterize distinguishable inshore systems. The high variability at the shallow sampling sites prevents, however a simple resolution of the seasonal courses. Light dose could be identified as a potential key in order to describe long-term variations of N-uptake at the station with higher organic matter concentration (station KW), but phytoplankton development is better reflected in the seasonal course of N-uptake at the other station. Specific nitrogen uptake rates (NH4
+: 0.0009–0.0353 h–1, urea: 0.0001–0.0137 h–1, NO3
–: 0.000004–0.0009 h–1) and relative nitrogen preferences indicate extraordinary importance of reduced nitrogenous nutrients (NH4
+, urea) at both stations throughout the year. 相似文献
14.
The microsomal fraction isolated from dog mesenteric nerve fibres was found to contain ATPase activity stimulated by micromolar concentrations of Ca ions. Such a high-affinity Ca2+-ATPase (hereafter referred to as HA Ca-ATPase) followed a Michaelis-Menten kinetics with Km for Ca ions of 0.4 M and Vmax=12.5±2.4 mol Pi.mg–1h–1. The examination of the subcellular origin of HA Ca-ATPase revealed that this enzyme is associated with axonal plasma membranes as documented by its co-purification with several plasma membrane marker enzymes and with tetrodotoxin-sensitive3H-saxitoxin binding. The addition of exogenous magnesium ions (Mg) resulted in a non-competitive inhibition of HA Ca-ATPase with Ki=0.5 mM. The reaction velocity of HA Ca-ATPase was also inhibited by other divalent ions with the order of potency Mg>Mn >ZnCo>Ni. In contrast to low affinity (high Km) Mg- and Ca-ATPase, the HA Ca-ATPase was insensitive to the inhibition by sodium azide (10 mM) and sodium fluoride (10 mM). Similarly, the specific activity of HA Ca-ATPase was unaffected by vanadate (100 M) and N-ethylmaleinimide (100 M). It is concluded that axonal plasma membranes of dog mesenteric nerves contain HA Ca-ATPase which seems to be unrelated to calcium-transporting Mg-dependent, Ca-stimulated ATPase.Abbreviations used BSA
bovine serum albumin
- HA Ca-ATPase
high-affinity Ca2+-ATPase
- K-pNPPase
onabain-sensitive, K+-stimulated p-nitrophenyl phosphatase
- NEM
N-ethylmaleinimide
- SIM
250 mM sucrose, 10 mM imidazole-HCl pH 7.4
- TRIS
tris (hydroxymethyl) aminomethane 相似文献
15.
Summary This communication reports the kinetics of the Na+/ Ca2+ exchanger and of the plasma membrane (PM) Ca2+ pump of the intact human platelet. The kinetic properties of these two systems were deduced by studying the rate of Ca2+ extrusion and its Na+ dependence for concentrations of cytoplasmic free Ca2+ ([Ca2+]cyt) in the 1–10-m range. The PM Ca2+ATPase was previously characterized (Johansson, J.S. Haynes, D.H. 1988. J. Membrane Biol.
104:147–163) for [Ca2+]cyt] 1.5 m with the fluorescent Ca2+ indicator quin2 (K
d= 115 nm). That study determined that the PM Ca2+ pump in the basal state has a V
max = 0.098 mm/min, a K
m= 80 nm and a Hill coefficient = 1.7. The present study extends the measurable range of [Ca2+]cyt with the intracellular Ca2+ probe, rhod2 (K
d= 500 nm), which has almost a fivefold lower affinity for Ca2+. An Appendix also describes the Mg2+ and pH dependence of the K
dand fluorescence characteristics of the commercially available dye, which is a mixture of two molecules. Rates of active Ca2+ extrusion were determined by two independent methods which gave good agreement: (i) by measuring Ca2+ extrusion into a Ca2+-free medium (above citation) or (ii) by the newly developed ionomycin short-circuit method, which determines the ionomycin concentration necessary to short circuit the PM Ca2+ extrusion systems. Absolute rates of extrusion were determined by knowledge of how many Ca2+ ions are moved by ionomycin per minute. The major findings are as follows: (i) The exchanger is saturable with respect to Ca2+ with a K
m= 0.97 ± 0.31 m and Vmax = 1.0 ± 0.6 mm/ min. (ii) At high [Ca2+]cyt, the exchanger works at a rate 10 times as large as the basal V
max of the PM Ca2+ extrusion pump. (iii) The exchanger can work in reverse after Na+ loading of the cytoplasm by monensin. (iv) The PM Ca2+ extrusion pump is activated by exposure to [Ca2+]cyt 1.5 m for 20–50 sec. Activation raises the pump V
max to 1.6 ± 0.6 mm/min and the K
mto 0.55 ± 0.24 m. (v) The Ca2+ buffering capacity of the cytoplasm is 3.6 mm in the 0.1 to 3 m range of [Ca2+]cyt. In summary, the results show that the human platelet can extrude Ca2+ very rapidly at high [Ca2+]cyt. Both the Na+/Ca2+ exchanger and Ca2+ pump activation may prevent inappropriate platelet activation by marginal stimuli.Abbreviations cAMP
cyclic adenosine 3,5-monophosphate
- cGMP
cyclic guanosine 3,5,-monophosphate
- Ca-CAM
calcium calmodulin;
- DT
dense tubules
- B
intrinsic cytoplasmic Ca2+ binding sites
- R
rhod2 or 5-(3,6-bis(dimethylamino)xanth-9-yl)-1-(2-amino-4-hy droxy lphenoxy)-2-(2-amino-5-methylphen- oxy)ethane-N,N,NN-tetraacetic acid
- [Ca2+]cyt
cytoplasmic Ca2+ activity
- quin2
2-[[2-bis[(carboxymethyl)amino]-5-methyl-phenoxy]methyl]-6-methoxy-8-[bis(carboxymethyl)amino]quinoline
- V or Vextrusion
true rate of Ca2+ extrusion
- fura-2
1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,NN-tetraacetic acid
- AM
acetoxymethyl ester
- DMSO
dimethylsulfoxide
- CTC
chlortetracycline
- EGTA
ethyleneglycol-bis(-aminoethyl ether) N,N,N,N- tetraacetic acid
- HEPES
4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid
- NMDG
N-methyl-d-glucamine
- PIPES
1,4-piperazine-bis-(ethanesulfonic acid)
- HPLC
high performance liquid chromatography
- I
fraction of high-affinity rhod2 complexed with Ca2+
-
F
the observed fluorescence
- Fmin
the minimal fluorescence observed in the absence of Ca2+
- Fmax
the maximal fluorescence observed when the dye is saturated with Ca2+
- X1
the fraction of high-affinity dye
-
K
d,1
dissociation constant of high-affinity dye
-
K
d,2
dissociation constant of the low-affinity dye
- -d1/dt
rate of Ca2+ removal from the rhod2-Ca complex;
- -dF/dt
the slope representing the absolute rate of fluorescence decrease in a progress curve
- Fmax
(Fmax — Fmin)cyt difference between maximal and minimal fluorescence for cytoplasmic high affinity form of rhod2
- F50
fluorescence of the high-affinity form ofrhod2for[Ca2+]cyt=50 nM
- [Ca2+]0
external Ca2+concentration
-
K
p
proportionality constant between the total number of Ca2+ ions moved and the change in high-affinity rhod2 complexation to Ca2
- (d[Ca2+]cyt, T)/dt
rate of Ca2+ influx obtained with maximal levels of ionomycin
- kleak
rate constant for passive inward Ca2+ leakage
- kinno
rate constant for ionomycin-mediated Ca2+ influx
- T
total
- [rhod2]cyt,T
total intracellular rhod2 concentration
- [quin2]cyt,T
total intracellular quin2 concentration
- [B]T
total cytoplasmic buffering capacity
- A[Ca2+]cyt,T
total number of Ca2+ ions moved into the cytoplasm
- [rhod2-Ca]cyt, T
change in concentration of total intracellular high-affinity rhod2 complexed to Ca2+
- [B-Ca]T
change in concentration of total cytoplasmic binding sites complexed to Ca2+
- [quin2]cyt, T
change in concentration of total intracellular quinl complexed to Ca2+
-
change in the degree of intracellular quin2 saturation
- 1
change in degree of saturation of cytoplasmic high-affinity rhod2
- 1-/t
rate of change in degree of saturation of cytoplasmic high affinityrhod2
- Vobs
observed rate of Ca2+ removal from the rhod2-Ca complex
- V8.3 m
the rate of Ca2+ removal from the high affinity rhod2-Ca complex at [Ca2+]cyt = 8.3 m
- /t
rate of change in of the degree of quin2 saturation
- [Ca2+]cytT/t
initial linear rate of ionomycin-mediated Ca2+ influx
- EC50
effective concentration giving a half-maximal effect
- [Na+]cyt
cytoplasmic Na+ activity
- CAM
calmodulin
- ACN
acetonitrile
- TFA
trifuloroacetic acid 相似文献
16.
Rivka Goldshleger Guy Patchornik Meirav Bar Shimon Daniel M. Tal Robert L. Post Steven J. D. Karlish 《Journal of bioenergetics and biomembranes》2001,33(5):387-399
This chapter describes contributions of transition metal-catalyzed oxidative cleavage of Na+,K+-ATPase to our understanding of structure–function relations. In the presence of ascorbate/H2O2, specific cleavages are catalyzed by the bound metal and because more than one peptide bond close to the metal can be cleaved, this technique reveals proximity of the different cleavage positions within the native structure. Specific cleavages are catalyzed by Fe2+ bound at the cytoplasmic surface or by complexes of ATP–Fe2+, which directs the Fe2+ to the normal ATP–Mg2+ site. Fe2+- and ATP–Fe2+-catalyzed cleavages reveal large conformation-dependent changes in interactions between cytoplasmic domains, involving conserved cytoplasmic sequences, and a change of ligation of Mg2+ ions between E1P and E2P, which may be crucial in facilitating hydrolysis of E2P. The pattern of domain interactions in E1 and E2 conformations, and role of Mg2+ ions, may be common to all P-type pumps. Specific cleavages can also be catalyzed by Cu2+ ions, bound at the extracellular surfaces, or a hydrophobic Cu2+-diphenyl phenanthroline (DPP) complex, which directs the Cu2+ to the membrane–water interface. Cu2+- or Cu2+-DPP-catalyzed cleavages are providing information on / subunit interactions and spatial organization of transmembrane segments. Transition metal-catalyzed cleavage could be widely used to investigate other P-type pumps and membrane proteins and, especially, ATP binding proteins. 相似文献
17.
Collagenase treatment, commonly used to prepare alkaline phosphatase-rich matrix vesicles from epiphyseal cartilage growth plates, seems to affect the integrity of this membrane-bound enzyme. Alkaline phosphatase-rich rat osseous plates were incubated with 1000 U/mL collagenase for 3 h, at 37°C and after purification on Sepharose 4B, kinetic studies were performed using nitrophenylphosphate and pyrophosphate as substrates.The optimum apparent pH for the hydrolysis of p-nitrophenylphosphate and pyrophosphate increased from 9.4 to 10.25 and from 8.0 to 9.0, respectively, as a consequence of collagenase treatment. In the absence of Mg2+ ions, the enzyme hydrolyzed PNPP with KM = 322.5 ± 15.3 M and V = 965.2 ± 45.8 U/mg, while in the presence of 2 mM Mg2+ ions, V increased 66%. Cobalt (K0.5 = 5.3 ± 0.3 M) and manganese (K0.5 = 0.72 ± 0.03 M) ions stimulated the PNPPase activity of the collagenase-treated enzyme, but with a lower apparent affinity when compared with that of not-treated enzyme. In the absence of Mg2+ ions pyrophosphate was hydrolyzed according to Michaelis-Menten kinetics (KM = 105.1 ± 6.3 M and V = 64.9 ± 3.9 U/mg), but site-site interactions (nH = 1.2) were observed in the presence of 2 mM Mg2+ ions (V = 110.8 ± 5.5 U/mg; K0.5 = 42.7 ± 2.0 M).To our knowledge this is the first report showing significant alterations on phosphohydrolytic activity and metal binding properties of bone alkaline phosphatase due to associated neutral proteases in collagenase preparations often used for the isolation of matrix vesicles. 相似文献
18.
Frank Thévenod Martine Dehlinger-Kremer Thomas P. Kemmer Anna-Luise Christian Barry V. L. Potter Irene Schulz 《The Journal of membrane biology》1989,109(2):173-186
Summary We have measured Ca2+ uptake and Ca2+ release in isolated permeabilized pancreatic acinar cells and in isolated membrane vesicles of endoplasmic reticulum prepared from these cells. Ca2+ uptake into cells was monitored with a Ca2+ electrode, whereas Ca2+ uptake into membrane vesicles was measured with45Ca2+. Using inhibitors of known action, such as the H+ ATPase inhibitors NBD-Cl and NEM, the Ca2+ ATPase inhibitor vanadate as well as the second messenger inositol 1,4,5-trisphosphate (IP3) and its analog inositol 1,4,5-trisphosphorothioate (IPS3), we could functionally differentiate two non-mitochondrial Ca2+ pools. Ca2+ uptake into the IP3-sensitive Ca2+ pool (IsCaP) occurs by a MgATP-dependent Ca2+ uptake mechanism that exchanges Ca2+ for H+ ions. In the absence of ATP Ca2+ uptake can occur to some extent at the expense of an H+ gradient that is established by a vacuolar-type MgATP-dependent H+ pump present in the same organelle. The other Ca2+ pool takes up Ca2+ by a vanadate-sensitive Ca2+ ATPase and is insensitive to IP3 (IisCaP). The IsCaP is filled at higher Ca2+ concentrations (10–6 mol/liter) which may occur during stimulation. The low steady-state [Ca2+] of 10–7 mol/liter is adjusted by the IisCaP.It is speculated that both Ca2+ pools can communicate with each other, the possible mechanism of which, however, is at present unknown. 相似文献
19.
M. A. Khan 《Hydrobiologia》1986,135(3):233-242
L. Naranbagh (alt. 1587 m) is a polymictic, shallow marl lake in the flood-plain valley of Kashmir, India. Macrofloral affinities resemble Potamogeton Type of Forsberg (1965) with alkaline waters, not rich in phosphorus. CaCO3 precipitation coupled with decline in Ca2+ and alkalinity values are characteristic of the lake. Fluctuations in Mg2+, Na+, K+, and Cl– were relatively conservative. The levels of PO
inf4
sup3–
-P and NO
inf3
sup–
-N indicate moderate fertility of the lake water.Persistence of a summer-autumn planktonic algal pulse is related to favourable irradiance, high water temperatures, and increased photosynthetic efficiency values. The most striking seasonality in photosynthetic rates (m–2 h–1) between winter minimum (3 mg Cassim) and summer maximum (75.4 mg Cassim) is determined by mainly climatic changes. Energy flow gave annual phytoplankton production of 51.95 × 102 KJ m–2 for the ecosystem.The nutrient levels and productivity rates suggest mesotrophic status of L. Naranbagh in classic oligoeutrophic classification of lake types. 相似文献
20.
Deborah Dixon Adrian Corbett Duncan H. Haynes 《Journal of bioenergetics and biomembranes》1982,14(2):87-96
The ability of the Ca2+-Mg2+ ATPase pump of skeletal SR to produce and maintain a Ca2+ gradient was studied as a function of the ATP/ADP/Pi ratio. The internal free Ca2+ concentration [Ca2+]i was monitored by changes in fluorescence of CTC. Increasing ADP concentrations in the medium reduce the maximal [Ca2+]i concentration achieved. The inclusion or the omission of 4×10–4 M Pi or doubling the absolute ATP and ADP concentrations at a constant ATP/ADP ratio does not affect the level obtained. The level depends primarily on the ATP/ADP ratio. The [Ca2+] concentration shows a 1.5 power dependence on the ATP/ADP ratio. Further, [Ca2+]i achieved at steady state does not depend on whether the pump had been working in the forward or the reverse direction prior to testing. Analysis shows that the levels of Ca2+ achieved are much lower than the levels predicted thermodynamically under the assumption of ideal coupling between Ca2+ transport and ATP hydrolysis with a stoichiometry of 2:1. Under this condition the osmotic energy of the [Ca2+]i/[Ca2+]o ratio was shown to be 48% as large as the free energy of hydrolysis of ATP, giving an overall thermodynamic efficiency of 48%. Analysis shows that maximal steady-state uptake is determined by the balance between the rates of uptake by the pump and rates of leak processes (intrinsic or extrinsic to the pump). Comparison with other studies shows that the [Ca2+]i achieved results in trans-inhibition of the pump by tying up the Ca2+ translocator in the inwardly oriented phosphorylated form. The absence of an effect of Pi can be taken as evidence that the dissociation of Ca2+ from the inwardly oriented translocator on the phosphoylated enzyme must precede the dephosphorylation of the enzyme. 相似文献