首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Rotational diffusion properties have been derived for the DNA dodecamer d(CGCGAATTCGCG)2 from 13C R1 and R1 measurements on the C1, C3, and C4 carbons in samples uniformly enriched in 13C. The narrow range of C-H bond vector orientations relative to the DNA axis make the analysis particularly sensitive to small structural deviations. As a result, the R1/R1 ratios are found to fit poorly to the crystal structures of this dodecamer, but well to a recent solution NMR structure, determined in liquid crystalline media, even though globally the structures are quite similar. A fit of the R1/R1 ratios to the solution structure is optimal for an axially symmetric rotational diffusion model, with a diffusion anisotropy, D||/D, of 2.1±0.4, and an overall rotational correlation time, (2D||+4D)–1, of 3.35 ns at 35 °C in D2O, in excellent agreement with values obtained from hydrodynamic modeling.  相似文献   

2.
Ca,phospholipid-dependent (PKC) andcAMP-dependent (PKA) protein kinases phosphorylate the -subunit of the Na,K-ATPase from duck salt gland with the incorporation of 0.3 and 0.5 mol32P/mol of -subunit, respectively. PKA (in contrast to PKC) phosphorylates the -subunit only in the presence of detergents. Limited tryptic digestion of the Na,K-ATPase phosphorylated by PKC demonstrates that32P is incorporated into the N-terminal 41-kDa fragment of the -subunit. Selective chymotrypsin cleavage of phosphorylated enzyme yields a 35-kDa radioactive fragment derived from the central region of the -subunit molecule. These findings suggest that PKC phosphorylates the -subunit of the Na,K-ATPase within the region restricted by C3 and T1 cleavage sites.  相似文献   

3.
This study reports a novel splice variant form of the voltage-dependent calcium channel 2 subunit (2g). This variant is composed of the conserved amino-terminal sequences of the 2a subunit, but lacks the -subunit interaction domain (BID), which is thought essential for interactions with the 1 subunit. Gene structure analysis revealed that this gene was composed of 13 translated exons spread over 107 kb of the genome. The gene structure of the 2 subunit was similar in exon-intron organization to the murine 3 and human 4 subunits. Electrophysiological evaluation revealed that 2a and 2g affected channel properties in different ways. The 2a subunit increased the peak amplitude, but failed to increase channel inactivation, while 2g had no significant effects on either the peak current amplitude or channel inactivation. Other subunits, such as 3 and 4, significantly increased the peak current and accelerated current inactivation.  相似文献   

4.
An improved method is introduced for the determination of the quantum yield of photosystem I. The new method employs saturating light pulses with steep rise characteristics to distinguish, in a given physiological state, centers with an open acceptor side from centers with a reduced acceptor side. The latter do not contribute to PSI quantum yield (I). Oxidation of P700 is measured by a rapid modulation technique using the absorbance change around 830 nm. The quantum yield I is calculated from the amplitude of the rapid phase of absorbance change (A; 830 nm) upon application of a saturation pulse in a given state, divided by the maximal A (830 nm) which is induced by a saturation pulse with far-red background illumination. Using this technique, I can be determined even under conditions of acceptor-side limitation, as for example in the course of a dark-light induction period or after elimination of CO2 from the gas stream. Thus determined I values display a close-to-linear relationship with those for the quantum yield of PSII (II) calculated from chlorophyll fluorescence parameters. It is concluded that the proposed method may provide new information on the activity of the PSI acceptor side and thus help to separate the effects of acceptorside limitation from those of cyclic PSI, whenever a non-linear relationship between II and the P700-reduction level is observed.Abbreviations and Symbols A absorbance change - I quantum yield of photosystem I - II quantum yield of photosystem II - PAR photosynthetically active radiation This work was supported by the Deutsche Forschungsgemeinschaft (SFB 176 Molekulare Grundlagen der Signalübertragung und des Stofftransportes in Membranen and SFB 251 Ökologie, Physiologie und Biochemie pflanzlicher Leistung unter Streß).  相似文献   

5.
Evidence from ventricular preparations of cat, sheep, rat and dog suggests that both 1-adrenoceptors (1AR) and 2-adrenoceptors (2AR) mediate positive inotropic effects but that only 1AR do it through activation of a cAMP pathway. On the other hand, our evidence has shown that both 1 AR and 2 AR hasten relaxation of isolated human myocardium consistent with a common cAMP pathway. We have now investigated in the isolated human right atrial appendage, a tissue whose -AR comprise around 2/3 of 1AR and 1/3 of 2AR, whether or not 2AR-mediated effects occur via activation of a cAMP pathway. We carried out experiments on atria obtained from patients without advanced heart failure undergoing open heart surgery. To activate 2AR, we used the 2AR-selective ligand zinterol. Experiments were carried out on paced atrial strips (1 Hz) and tissue homogenates and membrane particles. Zinterol caused positive inotropic and lusitropic (i.e. reduction of t1:2 of relaxation) effects with EC50 values of 3 and 2 nM, respectively. The zinterol-evoked effects were unaffected by the AR-selective antagonist CGP 20712A (300 nM) but blocked surmountably by the 2AR-selective antagonist ICI 118551 (50 nM) which reduced both EC50 values to 1 M. Zinterol stimulated adenylyl cyclase activity with an EC50 of 30 nM and intrinsic activity of 0.75 with respect to (–)-isoprenaline (600 M); the effects were resistant to blockade by CGP 20712A (300 nM) but antagonised surmountably by ICI 118551 (50 nM). Zinterol bound to membrane PAR labelled with (–)-[125I] cyanopindolol with higher affinity for 2AR than for - 1 AR; the binding to 2AR but not to - BAR was reduced by GTPyS (10 M). In the presence of CGP 20712A (300 nM) (–)-isoprenaline (400 M); (to activate both 1AR and 2AR maximally) and zinterol (10 M); increased contractile force 3.4-fold and 2.5-fold respectively and reduced relaxation tut by 32% and 18% respectively. These effects of (–)-isoprenaline and zinterol were associated (5 min incubation) with phosphorylation (pmol P/mg supernatant protein) of troponin I and C-protein to values of 8.4 ± 2.0 vs 12.4 ± 2.3 and 10.1 ± 2.5 vs 8.6 ± 1.6 respectively. (–)-Isoprenaline and zinterol also caused phosphorylation of phospholamban (1.8 ± 0.3 vs 0.4 ± 0.1 pmol P/mg respectively) specifically at serine residues. We conclude that in human atrial myocardium activation of both 1AR and 2AR leads to cAMP-dependent phosphorylation of proteins involved in augmenting both contractility and relaxation.  相似文献   

6.
Summary A set of three 3D (1H, 13C, 15N) triple-resonance correlation experiments has been designed to provide H1-H8 intraresidue sugar-to-base correlations in purines in an unambiguous and efficient manner. Together, the HsCsNb, HsCs(N)bCb, and HbNbCb experiments correlate the H1 sugar proton to the H8 proton of the attached base by means of the {H1, C1, N9, C8, H8} heteronuclear scalar coupling network. The assignment strategy presented here allows for unambiguous H1-H8 intraresidue correlations, provided that no two purines have both the same H1 and C1 chemical shifts and the same C8 and N9 chemical shifts. These experiments have yielded H1-H8 intraresidue sugar-to-base correlations for all five guanosines in the [13C, 15N] isotopically labeled RNA duplex r(GGCGCUUGCGUC)2.  相似文献   

7.
Summary A single injection of -interferon (-IFN) (30 000 units/mouse), a major biological modifier of natural killer (NK) cytolytic activity, strongly stimulated NK activity in normal mice, as expected, while the same treatment did not statistically alter the NK response in cyclophosphamide (CY)-suppressed animals.We investigated the possibility of thymosin 1 cooperating with -IFN in boosting NK activity in CY-suppressed animals.The results show that treatment with thymosin 1 (200 g/kg) for 4 days, followed by a single injection of -IFN 24 h before testing, strongly restored NK activity in CY-suppressed mice. Thymosin 1 was, moreover, able to accelerate the recovery rate of NK activity in bone marrow reconstituted murine chimeras.Taken together the data support the concept that the synergic effect between thymosin 1 and -IFN could be the result of effects on differentiation of the NK lineage at different levels.  相似文献   

8.
A human HLA-DQ -chain cDNA was used as a probe to identify and isolate a rat major histocompatibility antigen -chain gene from a genomic library constructed in the vector Charon 28 using Wistar rat DNA (RT1 u). The isolated exon of the rat gene (RT1.B 2) encoding a -chain second domain was found to share 93% nucleotide homology with a mouse A 2 exon. Although the genomic organization of this gene is consistent with the hypothesis that it represents a pseudogene, the remarkable preservation of a specific sequence favors the view that this class II antigen -chain gene has retained its coding function.  相似文献   

9.
Summary [13C5]-2-Deoxy-d-ribose, synthesized from [13C6]-d-glucose (98% 13C), was coupled with thymine to give [1,2,3,4,5-13C5]-thymidine (T) in an 18% overall yield. The thymidine was converted to the 3-phosphoramidite derivative and was then incorporated into a dodecamer 5-d(CGCGAATTCGCG)-3 by solid-phase DNA synthesis. Preparation of 0.24 mole of the labeled dodecamer, which is sufficient for a single NMR sample, consumed only 25 mg of glucose. By virtue of the 13C labels, all of the 1H-1H vicinal coupling constants in the sugar moieties were accurately determined by HCCH-E.COSY.  相似文献   

10.
The low-copy-number and broad-host-range pSM19035-derived plasmid pBT233 is stably inherited in Bacillus subtilis cells. Two distinct regions, segA and segB, enhance the segregational stability of the plasmid. Both regions function in a replicon-independent manner. The maximization of random plasmid segregation is accomplished by the recombination proficiency of the host or the presence of the pBT233 segA region. The segA region contains two open reading frames (or) [ and ]. Inactivation or deletion of or results in SegA plasmids. Better than random segregation requires an active segB region. The segB region contains two ors (or and or). Inactivation of either of the orfs does not lead to an increase in cell death, but or plasmids are randomly segregated. These results suggest that pBT233 stabilization relies on a complex system involving resolution of plasmid oligomers (segA) and on the function(s) encoded by the segB region.  相似文献   

11.
The reaction of methanol dehydrogenase with cytochrome c L from Methylophaga marina and the reactions of the non-physiological substrates, Wurster's blue and ascorbic acid, with both proteins were studied as a function of temperature (4–32 °C), pressure (1–2000 bar) and ionic strength using the optical high pressure stopped-flow method. The thermodynamic parameters H, S and V were determined for all reactions where electron transfers are involved. These data allowed the determination of the Maxwell relationships which proved the internal thermodynamic consistency of the system under study. A conformational change on the cytochrome c L level was deduced from both breaks in the Arrhenius plots and the variation of the V with temperature.Abbreviations MOPS 4-morpholinepropanesulfonic acid - CHES 2-(cyclohexylamino)ethanesulfonic acid - MDH methanol dehydrogenase - EDTA ethylenedinitrilotetraacetic acid disodium salt - BTB bromothymol blue (3,3-dibromothymolsulfoneph-thalein) - PQQ 2,7,9-tricarboxy-lH-pyrrolo-[2,3f]quinoline-4,5-dione - cytochrome c HH mammalian horse heart cytochrome c  相似文献   

12.
Summary Recombinant cDNA plasmids possessing the coding sequences for the -type gliadins were isolated from a cDNA library prepared from wheat seed poly (A+) RNA. One of these plasmids, pGliB48, specifically hybridizes to poly (A+) RNA molecules 1 400–1 500 bases in length that direct the synthesis of polypeptides at 38 Kd and 46 Kd, the latter size characteristic of the -type gliadins. The cDNA sequence of pGliB48 was determined and encompasses the 3 untranslated region as well as 245 amino acids from the C-terminus of the -type gliadin polypeptide. The 5-end of the DNA coding sequence consists of a tandem repeat unit composed of eight amino acids. Localized regions of homology are observed for the /-type and -type gliadin cDNA sequences.  相似文献   

13.
Synopsis Length-frequency data suggest Nile perch, Lates niloticus, from the Nyanza Gulf grew to a total length of 9 cm by age 118 days and 23 cm by age 287 days. A modified von Bertalanffy growth curve t = 1.35·L(1-e–K(t-t o)) with the parameters L = 93.1, K = 0.272 and to = 0.046, is suggested to describe growth up to 5 years of age and the relationship t = 1.35·(31.96 + 7.681t) for fish aged 6 years and above. Length-weight relationships were = 0.0234·-gt2.74 for fish between 7 and 15.9 cm total length, = 0.0151·2.94 for fish between 16 and 45.9 cm total length, and = 0.0023·3.44 for fish between 46 and 120 cm total length. Male Nile perch first matured between 50 and 55 cm total length when they were probably 2 years old; female Nile perch first matured between 80 and 85 cm total length when they were probably 4 years old. Small males were common, large males were rare, with the reverse holding for females. Sex change, from male to female, is a possible explanation for this size dimorphism.  相似文献   

14.
Recently, we have developed an analytical, semi-microscopic theory for the macroscopic behavior of a solvent-containing black lipid film subjected to an electric cross film voltage, . Here we employ the theoretical expressions derived for the disjoining pressure, D, the film elasticity, F, and the film tension, F, to construct the stability diagram of the film, in the D-. Depending on its state (D, ), the film is stable or is prone to squeezing or bending deformations. For a monooleate film we show how the destruction of the plane film due to a periodic thickness fluctuation (squeezing) is facilitated by two mechanisms: i) lowering of D at fixed ; ii) lowering of at fixed D, provided that the film is in a stable state characterized by D<–7.03×103 dyne/cm2 and >0 mV. Bending of a low tension film (single interface tension s 0.025 dyne/cm1) can be achieved only for >170 mV and D > –8.7 × 104 dyne/cm2. Finally, we demonstrate the existence of a marginal state ( D 0 , 0) where the film is predicted to exhibit strong fluctuations both in the squeezing and in the bending mode.  相似文献   

15.
Summary Determinations of current-voltage relationships are widely employed in the characterization of epithelial sodium transport. In order to determine the protocol dependence of transport parameters in the toad urinary bladder, studies were carried out in the presence and absence of amiloride, an inhibitor of active sodium transport. With symmetric positive and negative perturbations of the transepithelial electrical potential difference (0±100 mV) for 30 sec, the amiloride-sensitive current-voltage (i a -) relationship was near linear over the range –75+100 mV, indicating constancy of the conductance a and the apparent electromotive force E Na, lumped parameters of the standard electrical equivalent circuit model of the active transport system. With a reverse protocol (±1000 mV) or 15 min perturbations thei a - relationships were highly nonlinear. Nonlinearity reflected voltage dependence of parameters: perturbations that increased active transport decreased E Na and increased a, as evaluated from 10 sec perturbations of ; slowing of active transport produced the converse changes. These effects are usefully analyzed in both quasi-steady states and true steady states by means of a detailed equivalent circuit incorporating the significant ionic currents across each plasma membrane. Precise understanding of the significance of a and E Na will require characterization of the partial ionic conductances on perturbation of .  相似文献   

16.
Crude extracts or supernatants of broken cells of Clostridium formicoaceticum reduce unbranched, branched, saturated and unsaturated carboxylates at the expense of carbon monoxide to the corresponding alcohols. The presence of viologens with redox potentials varying from E 0=-295 to-650 mV decreased the rate of propionate reduction. The more the propionate reduction was diminished the more formate was formed from carbon monoxide. The lowest propionate reduction and highest formate formation was observed with methylviologen. The carbon-carbon double bond of E-2-methyl-butenoate was only hydrogenated when a viologen was present. Formate as electron donor led only in the presence of viologens to the formation of propanol from propionate. The reduction of propionate at the expense of a reduced viologen can be followed in cuvettes. With respect to propionate Michaelis Menten behavior was observed. Experiments are described which lead to the assumption that the carboxylates are reduced in a non-activated form. That would be new type of biological reduction.Non-standard abbreviations glc Gas liquid chromatography - HPLC high performance liquid chromatography - RP reverse phase; Mediators (the figures in parenthesis of the mediators are redox potentials E 0 in mV) - CAV2+ carbamoylmethylviologen, 1,1-carbamoyl-4,4-dipyridinium dication (E 0=-296 mV) - BV2+ benzylviologen, 1,1-dibenzyl-4,4-dipyridinium dication (E 0=-360 mV) - MV methylviologen, 1,1-dimethyl-4,4-dipyridinium-dication (E 0=-444 mV) - DMDQ2+ dimethyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-ethylendication (E 0=-514 mV) - TMV2+ tetramethylviologen, 1,1,4,4-tetramethyl-4,4-dipyridinium dication (E 0=-550 mV) - PDQ2+ propyldiquat, 2,2-dipyridino-1,1-propenyl dication (E 0=-550 mV) - DMPDQ2+ dimethylpropyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-propenyl dication (E 0=-656 mV) - PN productivity number=mmol product (obtained by the uptake of one pair of electrons) x (biocatalyst (dry weight) kg)-1×h-1  相似文献   

17.
Summary The angular dependence of1JC,H in model compounds related to -linked oligosaccharides has been established by FPT INDO quantum chemical calculations. Values calculated for models of (1 1)-, (1 2)-, (1 3)- and (1 4)-linked disaccharides were compared, and the effect of the orientation of HO-2 elucidated. The angular dependence of1JC,H on the torsional angles H and H and the solvent dielectric constant (s) was characterized in the form:1JC,H = A cos2+B cos + C sin2 + D since + E + Fe. The1JC,H values, measured by DEPT methods for C-1-H-1 and C-X-H-X in cellobiose, cyclic trisaccharide and hexopyranoses were used to adjust the calculated angular dependences. Based on the occurrence of the conformers for agarobiose, neoagarobiose, mannobiose and methyl -xylobioside, the thermodynamically averaged <1JC,H > values were calculated. The results obtained (<1JC-1,H-1 > 162.4, <1JC-4, H-4 > 147.6 Hz for methyl -xylobioside; <1JC-1,H-1 > 162.4 and <1JC-4,H-4] > 147.6 Hz for mannobiose; <1JC-1,H-1 > 162.8 Hz for neo agarobiose and <1JC-1,H-1 > 163.2 Hz for agarobiose) agree well with the experimental values of 162.7, 147.5, 160.4, 147.2, 160.9 and 165.7 Hz, respectively.  相似文献   

18.
Experimental data relating to the breakage of isoelectric Soya protein precipitates in a mechanically agitated bioreactor are provided and examined in the light of a proposed mechanistic model which relates the size of the maximum attainable aggregate diameter to the energy dissipation rate in the vessel. The analysis suggests that protein precipitation results in the formation of scale-invariant fractal aggregates with a dimensionality of 2.2. Comparing the fractal dimensionality of the protein precipitates with reported values based on computer simulation studies suggests that the aggregates undergo considerable restructuring during agitation.List of Symbols A Hamaker constant (J) - D impeller diameter (m) - d p primary particle diameter (m) - d f maximum aggregate diameter (m) - G shear rate (s–1) - H 0 separation distance between two primary particles (m) - k constant in Eq. (5) - K constant in Eq. (6) - N impeller speed (rpm or rps) - r radial position in an aggregate, measured from the centre (m) - t time of exposure to shear (mins) - T e eddy period (s–1) - v f aggregate volume (m3) Greek Symbols aggregate dimensionality constant - energy dissipation rate (W/kg) - dynamic viscosity of particle-free liquid (kg/ms) - kinematic viscosity of particle-free liquid (m2/s) - collision probability (–) - p aggregate density (kg/m3) - p continuous phase density (kg/m3) - aggregate mechanical strength (N/m2) - shear stress (N/m2) - particle concentration in an aggregate (m3/m3) - (r) porosity at radial position, r  相似文献   

19.
In the present report, we used serological, cellular, and restriction fragment length polymorphism (RFLP) to investigate the DR1 haplotype in the Israeli population. We describe an Israeli homozygous typing cell (HTC), HLA-DwLVA, which defines a new lymphocyte-activating determinant associated with Bw65, DR1 and distinct from Dwl. The parents of this donor, non-Ashkenazi Algerian Jews, are first cousins and share HLA-Cw8, Bw65, BfS, DR1, DQw1, DPw4. No specificity could be assigned to HLA-DwLVA using the 91 Ninth Workshop HTCs. Two families and forty unrelated DR1 individuals were studied with DwLVA and a panel of DR1/Dw1 HTCs. HLA-DwLVA showed segregation as a single determinant within families. This new specificity was present in 24 out of 40 (60%) unrelated DR1 individuals, indicating that in the Israeli population DwLVA is the main lymphocyte-defined determinant associated with the serologically defined DRI specificity, in contrast to non-Jewish Caucasoids where DR1 is significantly associated with Dw1. The vast majority of DwLVA-positive carriers were also Bw65 carriers, indicating that Bw65, DR1, DwLVA may represent a typical allele combination in the Israeli population. The RFLP analysis established the correlation of certain RFLPs with Dw1 and DwLVA. In addition, we describe a cluster of RFLPs that may correspond to a new Dw subtype associated with DR1, for which no serological and cellular reagents have been described so far.  相似文献   

20.
Model membranes with unsaturated lipid chains containing various amounts of M13 coat protein in the -helical form were studied using time-resolved fluorescence and ESR spectroscopy. The lipid-to-protein (L/P) ratios used were > 12 to avoid protein-protein contacts and irreversible aggregation leading to -polymeric coat protein. In the ESR spectra of the 12-SASL probe in dioleoyl phosphatidylcholine (DOPC) bilayers no second protein induced component is observed upon incorporation of M13 coat protein. However, strong effects are detected on the ESR lineshapes upon changing the protein concentration. The ESR lineshapes are simulated by assuming a fixed ratio between the parallel (D) and perpendicular (D) diffusion coefficients of 4, and an order parameter equal to zero. It is found that increasing the protein concentration from L/P to L/P 15 results in a decrease of the rotational diffusion coefficient D from 3.4 × 107 to 1.9 × 107 s–1. In the time-resolved fluorescence experiments with DPH-propionic acid as a probe, it is observed that increasing the M13 coat protein concentration causes an increase of the two fluorescent lifetimes, indicating an increase in bilayer order. Analysis of the time-resolved fluorescence anisotropy decay allows one to quantitatively determine the order parameters P2 and P4, and the rotational diffusion coefficient D of the fluorescent probe. The order parameters P2 and P4 increase from 0.34 to 0.55 and from 0.59 to 0.77, respectively, upon adding M13 coat protein to DOPC bilayers with an L/P ratio of 35. The rotational diffusion coefficient D of the DPH-propionic acid probe decreases on incorporating M13 coat protein, in accordance with the ESR results. It is concluded that M13 coat protein in the -monomeric state is not able to produce a long living lipid boundary shell and consequently an immobilization of the lipids. An overall effect on the lipids is induced, resulting in a reduction in the dynamics and an increase in average lipid order. The hydrophobic region of M13 coat protein is proposed to perfectly match the lipid bilayer, resulting in a relatively small distortion of the bilayer structure of the lipid system.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号