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1.
The light-induced Q
A
–
/QA FTIR difference spectra of Rb. sphaeroides and Rp. viridis show very broad positive bands of small amplitude peaking around 2750 cm–1. Upon 1H/2H exchange these bands shift to about 2150 cm–1. Similarly, the Q
B
–
/QB spectra exhibit broad continuum bands at 2600 and 2800 cm–1 shifting to 2100 and 2200 cm–1 in 2H2O for Rb. sphaeroides and Rp. viridis, respectively. These continuum bands are tentatively interpreted in terms of highly polarizable hydrogen bonds in a large web of polar bonds involving cofactors, amino acid residues, and structured water molecules. As a working hypothesis, we propose that the protons participating in this web redistribute upon quinone reduction, increasing their concentration around the newly formed charged species, and leading to net proton uptake. Assuming that the precise localization of the mobile protons is dependent on the local electrostatic, this model can explain the apparent discrepancies between some results of FTIR experiments and of electrostatic calculations. Notably, it could help rationalize the observation that mobile protons tend to localize on Glu L212 upon QB reduction in Rb. sphaeroides, while for QB reduction in Rp. viridis and for QA reduction in both Rb. sphaeroides and Rp. viridis, proton uptake by a small number of carboxylic residues is not supported by the FTIR data. 相似文献
2.
W. S. Caughey A. Dong V. Sampath S. Yoshikawa X. -J. Zhao 《Journal of bioenergetics and biomembranes》1993,25(2):81-91
IR spectra directly probe specific vibrators in bovine heart cytochromec oxidase, yielding quantitative as well as qualitative information on structures and reactions at these vibrators. C-O IR spectra reveal that CO binds to
as two conformers each in isolated immobile environments sensitive to Fe
a
and/or CuA oxidation state but remarkably insensitive to pH, medium, anesthetics, and other factors that affect activity. C-N IR spectra reveal that the one CN– that binds to fully and partially oxidized enzyme can be in three different structures. These structures vary in relative amounts with redox level, thereby reflecting dynamic electron exchange among Fe
a
, CuA, and CuB with associated changes in protein conformation of likely significance in O2 reduction and H+-pumping. Azide IR spectra also reflect redox-dependent long-range effects. The amide I IR bands, due to C-O vibrators of peptide linkages and composed of multiple bands derived from different secondary structures, reveal high levels of -helix (60%) and subtle changes with redox level and exposure to anesthetics. N2O IR spectra reveal that these anesthetic molecules at clinically relevant levels occupy three sites of different polarity within the enzyme as the enzyme is reversibly, but only partially, inhibited. 相似文献
3.
Di Donato M Cohen RO Diner BA Breton J van Grondelle R Groot ML 《Biophysical journal》2008,94(12):4783-4795
It is now quite well accepted that charge separation in PS2 reaction centers starts predominantly from the accessory chlorophyll BA and not from the special pair P680. To identify spectral signatures of BA, and to further clarify the process of primary charge separation, we compared the femtosecond-infrared pump-probe spectra of the wild-type (WT) PS2 core complex from the cyanobacterium Synechocystis sp. PCC 6803 with those of two mutants in which the histidine residue axially coordinated to PB (D2-His197) has been changed to Ala or Gln. By analogy with the structure of purple bacterial reaction centers, the mutated histidine is proposed to be indirectly H-bonded to the C9O carbonyl of the putative primary donor BA through a water molecule. The constructed mutations are thus expected to perturb the vibrational properties of BA by modifying the hydrogen bond strength, possibly by displacing the H-bonded water molecule, and to modify the electronic properties and the charge localization of the oxidized donor . Analysis of steady-state light-induced Fourier transform infrared difference spectra of the WT and the D2-His197Ala mutant indeed shows that a modification of the axially coordinating ligand to PB induces a charge redistribution of In addition, a comparison of the time-resolved visible/midinfrared spectra of the WT and mutants has allowed us to investigate the changes in the kinetics of primary charge separation induced by the mutations and to propose a band assignment identifying the characteristic vibrations of BA. 相似文献
4.
Tommy ?man May-Britt Tessem Tone F Bathen Helena Bertilsson Anders Angelsen Mattias Hedenstr?m Trygve Andreassen 《BMC bioinformatics》2014,15(1)
Background
Identification of individual components in complex mixtures is an important and sometimes daunting task in several research areas like metabolomics and natural product studies. NMR spectroscopy is an excellent technique for analysis of mixtures of organic compounds and gives a detailed chemical fingerprint of most individual components above the detection limit. For the identification of individual metabolites in metabolomics, correlation or covariance between peaks in 1H NMR spectra has previously been successfully employed. Similar correlation of 2D 1H-13C Heteronuclear Single Quantum Correlation spectra was recently applied to investigate the structure of heparine. In this paper, we demonstrate how a similar approach can be used to identify metabolites in human biofluids (post-prostatic palpation urine).Results
From 50 1H-13C Heteronuclear Single Quantum Correlation spectra, 23 correlation plots resembling pure metabolites were constructed. The identities of these metabolites were confirmed by comparing the correlation plots with reported NMR data, mostly from the Human Metabolome Database.Conclusions
Correlation plots prepared by statistically correlating 1H-13C Heteronuclear Single Quantum Correlation spectra from human biofluids provide unambiguous identification of metabolites. The correlation plots highlight cross-peaks belonging to each individual compound, not limited by long-range magnetization transfer as conventional NMR experiments.Electronic supplementary material
The online version of this article (doi:10.1186/s12859-014-0413-z) contains supplementary material, which is available to authorized users. 相似文献5.
A. Yu. Khmelnitskiy R. A. Khatypov A. M. Khristin M. M. Leonova L. G. Vasilieva V. A. Shuvalov 《Biochemistry. Biokhimii?a》2013,78(1):60-67
Primary charge separation dynamics in four mutant reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides with increased midpoint potential of the primary electron donor P (M160LH, L131LH, M197FH, and M160LH + L131LH + M197FH) have been studied by femtosecond transient absorption spectroscopy at room temperature. The decay of the excited singlet state in the wild-type and mutant RCs is complex and has two main exponential components, which indicates heterogeneity of electron transfer rates or the presence of reverse electron transfer reactions. The radical anion band of monomeric bacteriochlorophyll BA at 1020 nm was first observed in transient absorbance difference spectra of single mutants. This band remains visible, although with somewhat reduced amplitude, even at delays up to tens of picoseconds when stimulated emission is absent and the reaction centers are in the P+H A ? state. The presence of this band in this time period indicates the existence of thermodynamic equilibrium between the P+B A ? HA and P+BAH A ? states. The data give grounds for assuming that the value of the energy difference between the states P*, P+B A ? HA, and P+BAH A ? at early times is of the same order of magnitude as the energy kT at room temperature. Besides, monomeric bacteriochlorophyll BA is found to be an immediate electron acceptor in the single mutant RCs, where electron transfer is hampered due to increased energy of the P+B A ? state with respect to P*. 相似文献
6.
Paddock M.L. Senft M.E. Graige M.S. Rongey S.H. Turanchik T. Feher G. Okamura M.Y 《Photosynthesis research》1998,55(2-3):281-291
The structural basis for proton coupled electron transfer to QB in bacterial reaction centers (RCs) was studied by investigating RCs containing second site suppressor mutations (Asn M44 Asp, Arg M233 Cys, Arg H177 His) that complement the effects of the deleterious Asp L213 Asn mutation [DN(L213)]. The suppressor RCs all showed an increased proton coupled electron transfer rate k
AB
(2)(QA
–QB
– + H+ QAQBH–) by at least 103 (pH 7.5) and a recombination rate k
BD (D+QAQB
– DQAQB) 15–40 times larger than the value found in DN(L213) RCs. Proton transfer was studied by measuring the dependence of k
AB
(2) on the free energy for electron transfer (Get). k
AB
(2) was independent of Get in DN(L213) RCs, but dependent on Get in native and all suppressor RCs. This shows that proton transfer limits the k
AB
(2) reaction with a rate of 0.1s–1 in DN(L213) RCs but is not rate limiting and at least 108-fold faster in native and 105-fold faster in the suppressor RCs. The increased rate of proton transfer by the suppressor mutations are proposed to be due to: (i) a reduction in the barrier to proton transfer by providing a more negative electrostatic potential near QB
–; and/or (ii) structural changes that permit fast proton transfer through the network of protonatable residues and water molecules near QB. 相似文献
7.
The dinuclear bis(6-X-pyridin-2-olato) ruthenium complexes [Ru2(μ-XpyO)2(CO)4(PPh3)2] (X = Cl (4B) and Br (5B)), [Ru2(μ-XpyO)2(CO)4(CH3CN)2] (X = Cl (6B), Br (7B) and F (8B)) and [Ru2(μ-ClpyO)2(CO)4(PhCN)2] (9B) were prepared from the corresponding tetranuclear coordination dimers [Ru2(μ-XpyO)2(CO)4]2 (1: X = Cl; 2: X = Br) and [Ru2(μ-FpyO)2(CO)6]2 (3) by treatment with an excess of triphenylphosphane, acetonitrile and benzonitrile, respectively. In the solid state, complexes 4B-9B all have a head-to-tail arrangement of the two pyridonate ligands, as evidenced by X-ray crystal structure analyses of 4B, 6B and 9B, in contrast to the head-to-head arrangement in the precursors 1-3. A temperature- and solvent-dependent equilibrium between the yellow head-to-tail complexes and the red head-to-head complexes 4A-7A and 9A, bearing an axial ligand only at the O,O-substituted ruthenium atom, exists in solution and was studied by NMR spectroscopy. Full 1H and 13C NMR assignments were made in each case. Treatment of 1 and 2 with the N-heterocyclic carbene (NHC) 1-butyl-3-methylimidazolin-2-ylidene provided the complexes [Ru2(μ-XpyO)2(CO)4(NHC)], X = Cl (11A) or Br (12A). An XRD analysis revealed the head-to-head arrangement of the pyridonate ligands and axial coordination of the carbene ligand at the O,O-substituted ruthenium atom. The conversion of 11A and 12A into the corresponding head-to-tail complexes was not possible. 相似文献
8.
Summary Sequence-specific 1H and 15N resonance assignments have been made for 137 of the 146 nonprolyl residues in oxidized Desulfovibrio desulfuricans [Essex 6] flavodoxin. Assignments were obtained by a concerted analysis of the heteronuclear three-dimensional 1H-15N NOESY-HMQC and TOCSY-HMQC data sets, recorded on uniformly 15N-enriched protein at 300 K. Numerous side-chain resonances have been partially or fully assigned. Residues with overlapping 1HN chemical shifts were resolved by a three-dimensional 1H-15N HMQC-NOESY-HMQC spectrum. Medium-and long-range NOEs, 3JNH
coupling constants, and 1HN exchange data indicate a secondary structure consisting of five parallel -strands and four -helices with a topology similar to that of Desulfovibrio vulgaris [Hidenborough] flavodoxin. Prolines at positions 106 and 134, which are not conserved in D. vulgaris flavodoxin, contort the two C-terminal -helices.Abbreviations CSI
chemical shift index
- DQF-COSY
double-quantum-filtered correlation spectroscopy
- DIPSI
decoupling in the presence of scalar interactions
- FMN
flavin mononucleotide
- GARP
globally optimized alternating phase rectangular pulse
- HMQC
heteronuclear multiple-quantum coherence
- HSQC
heteronuclear single-quantum coherence
- NOE
nuclear Overhauser effect
- NOESY
nuclear Overhauser enhancement spectroscopy
- TOCSY
total correlation spectroscopy
- TPPI
time-proportional phase increments
- TSP
3-(trimethylsilyl)propionic-2,2,3,3-d
4 acid, sodium salt 相似文献
9.
Gopta Oksana A. Cherepanov Dmitry A. Mulkidjanian Armen Y. Semenov Alexey Yu. Bloch Dmitry A. 《Photosynthesis research》1998,55(2-3):309-316
Direct electrometry was used to study the light-induced voltage changes in the Rhodobacter sphaeroides chromatophores adsorbed to a phospholipid-impregnated nitrocellulose film. After the second laser flash, a fast increase in the voltage associated with charge separation was followed by a slower increase attributed to the proton uptake in the QB site of the photosynthetic reaction centers. Kinetics and relative amplitudes of these voltage changes attributed to the QA
–.
B
–. QAQBH2 transition, were measured as a function of pH and temperature between +4 and +40 °C. The kinetics can be approximated by a single exponent above +23 °C (100 µs at +25 °C, pH 7.2), whereas below this temperature, it was a good fit of two exponential approximation (65 µs and 360 µs with similar contributions at +10 °C, pH 7.2). The faster component diminished with an apparent pK 8.5, whereas the slower one was maintained at a constant level until pH 9.5 and then decreased. The calculated activation energy from the temperature dependence of the slower component (55 – 65 kJ/mol) was much higher than that of the faster component (< 10 kJ/mol). The two voltage components can be attributed to the transfer of the first (faster component) and the second (slower component) proton from the reaction center surface to QB. We suggested that higher activation energy of the slower component was due to a conformational change in the reaction center kinetically coupled to the second proton transfer to QBH–.The faster component diminished in the presence of 1 M KCl, with an apparent pK 7.5. To explain this observation, we assume that: (i) the midpoint potential of the QA/QA
–. redox pair was higher in 1 M KCl because of the reduced surface potential of chromatophores; (ii) the midpoint potential of the QB
–./QBH–. redox pair was insensitive to the surface potential change; (iii) the equilibrium constant of the reaction QA
–.QB
–. QAQBH– decreased at high ionic strength. 相似文献
10.
José Carreira José Manuel Andreu Manuel Nieto Emilio Muñoz 《Molecular and cellular biochemistry》1976,10(2):67-76
Summary Two new forms of the plasma membrane ATP-ase ofMicrococcus lysodeikticus NCTC 2665 were isolated from a sub-strain of the microorganism by polyacrylamide gel electrophoresis. One of them had a mol.wt of 368,000 and a very low specific activity (0.80 µ mol.min–1.mg protein–1) that could not be stimulated by trypsin. This form has been called BI (strain B, inactive). If the electrophoresis was carried out in the presence of reducing agents (i.e., dithiothreitol) and the pH of the effluent maintained at a value of 8.5 another form of the enzyme was obtained. This had a mol.wt of 385,000 and a specific activity of 2.5–5.0 µ mol.min–1.mg protein–1 that could be stimulated by trypsin to 5–10 µ mol.min–1.mg protein–1. This preparation of the ATPase has been called form BA (strain B, enzyme active). The subunit composition of both forms has been studied by sodium dodecyl sulphate and urea gel electrophoresis and compared to that of the enzyme previously purified from the original strain (form A). The three forms of the enzyme had similar and subunits, with mol.wt of about 50,000 and 30,000 dalton, respectively. They also had in common the component(s) of relative mobility 1.0, whose status as true subunit(s) of the enzyme remains yet to be established. However, subunit, that had a mol.wt of about a 52,500 in form A (Andreu
et al. Eur. J. Biochem. (1973) 37, 505–515), had a mol.wt similar to in form BI and about 60,000 in form BA. Furthermore BA usually showed two types of this subunit ( and) and an additional peptide chain () with a mol.wt of about 25,000 dalton. This latter subunit seemed to account for the stimulation by trypsin of form BA.Forms BA could be converted to BI by storage and freezing and thawing. Conventional protease activity could not be detected in any of the purified ATPase forms and addition of protease inhibitors to form BA failed to prevent its conversion to form BI. The low activity form (BI) was more stable than the active forms of the enzyme and also differed in its circular dichroism. These results show thatM. lysodeikticus ATPase can be isolated in several forms. Although these variations may be artifacts caused by the purification procedures, they provide model systems for understanding the structural and functional relationships of the enzyme and for drawing some speculations about its functionin vivo. 相似文献
11.
Reaction center-B875 pigment-protein complexes were purified from Rhodocyclus gelatinosus. The proteic components consist of 7–8 polypeptides among which some were identified by their apparent molecular weights: the light harvesting B875 polypeptides and of 8 and 6 kDa, reaction center L (23 kDa), M (28 kDa) and H (34 kDa), cytochrome c (43 kDa). Four c-type hemes were found per reaction center. Flash-induced absorbance changes showed the presence of both QA and QB in the complex. Charge recombination times were determined to be: 1.16±0.2 (n=30) for P+QAQB
- and 7–10 ms for P+QA
- in presence of herbicides. From quinone analysis on one hand and kinetics of charge recombination on the other hand, we proposed that in the reaction center of Rhodocyclus gelatinosus QA is menaquinone 8 and QB is ubiquinone 8. 相似文献
12.
Akihiko Himeno Kazuto Shigematsu Takashi Taguchi Masami Niwa 《Cellular and molecular neurobiology》1998,18(4):447-452
1. 125I-Endothelin (ET)-1 binding to the rat anterior pituitary gland was saturable and single, with a K
d of 71 pM and a B
max of 120 fmol/mg.2. When 1.0 M BQ-123 (ETA antagonist) was added to the incubation buffer, the binding parameters were 8.3 pM and 8.0 fmol/mg, whereas 10 nM sarafotoxin S6c (ETBagonist) exerted little change in these binding parameters (K
d,72pM;B
max, 110 fmol/mg).3. ETB receptor-related compounds such as sarafotoxin S6c, ET-3, IRL1620, and BQ-788 competitively inhibited 125I-ET-1 binding, only when 1.0 M BQ-123 was present in the incubation buffer.4. Thus, the ETB receptor is capable of binding ET-1 when the ETA receptor is being occupied by BQ-123. A collaboration mechanism between the ETA and the ETB receptor may function in the recognition of ET-1, a typical bivalent ligand. 相似文献
13.
Maria Letizia Trincavelli Chiara Giacomelli Simona Daniele Sabrina Taliani Barbara Cosimelli Sonia Laneri Elda Severi Elisabetta Barresi Isabella Pugliesi Giovanni Greco Ettore Novellino Federico Da Settimo Claudia Martini 《Biochimica et Biophysica Acta (BBA)/General Subjects》2014
Background
Among adenosine receptors (ARs) the A2B subtype exhibits low affinity for the endogenous agonist compared with the A1, A2A, and A3 subtypes and is therefore activated when concentrations of adenosine increase to a large extent following tissue damages (e.g. ischemia, inflammation). For this reason, A2B AR represents an important pharmacological target.Methods
We evaluated seven 1-benzyl-3-ketoindole derivatives (7–9) for their ability to act as positive or negative allosteric modulators of human A2B AR through binding and functional assays using CHO cells expressing human A1, A2A, A2B, and A3 ARs.Results
The investigated compounds behaved as specific positive or negative allosteric modulators of human A2B AR depending on small differences in their structures. The positive allosteric modulators 7a,b and 8a increased agonist efficacy without any effect on agonist potency. The negative allosteric modulators 8b,c and 9a,b reduced agonist potency and efficacy.Conclusions
A number of 1-benzyl-3-ketoindole derivatives were pharmacologically characterized as selective positive (7a,b) or negative (8c, 9a,b) allosteric modulators of human A2B AR.General significance
The 1-benzyl-3-ketoindole derivatives 7–9 acting as positive or negative allosteric modulators of human A2B AR represent new pharmacological tools useful for the development of therapeutic agents to treat pathological conditions related to an altered functionality of A2B AR. 相似文献14.
An experiment is presented which allows for the quantitative measurement of the relaxation interference between the 1HN CSA and 15N CSA interactions in 15N labeled proteins. A constant-time buildup scheme is used to measure the differential relaxation rate, , between double-quantum (DQ) and zero-quantum (ZQ) 1HN-15N coherences. The CSA/CSA experiment was recorded at three different Bo field strengths. The CSA(1HN)/CSA(15N) cross-correlation rate was obtained from the linear fit of the measured rate, , versus Bo
2 for 77 residues of the EH2 domain from mouse Eps15. 相似文献
15.
The slow oxidation of alkanes (from methane to hexane) in their stoichiometric mixtures with oxygen or air under the action of nanosecond pulsed discharges was investigated. The discharges were excited in a tube of diameter 5 cm and length of 20 cm by 25-ns voltage pulses with an amplitude of 10 kV and a repetition rate of 40 Hz. The initial pressure in the mixture was varied in the range 0.76–10.1 torr. The current, the electric field strength, and the power deposited in a discharge were measured with a nanosecond time resolution. In time-resolved and time-integrated measurements, the intensities of the following bands were determined: CO 2 + (B2Σ → X2Π, δv=0), CH(A2Δ, v′=0 → X2Π, v″=0), OH(A2Σ, v′=0 → X2Π, v″=0), CO(B1Σ, v′=0 → A1Π, v″=2), NO(A2Σ → X2Π, δv=3), N2(C3Π, v′=1 → B3Π, v″=7), N2(B3Π, v′=6 → A3Σ, v″=3), and N 2 + (B2Σ, v′=0 → X2Σ, v″=2). The methane concentration was measured from the absorption of He-Ne laser radiation. Based on the results of optical measurements, the times of the complete oxidation of hydrocarbons were determined. 相似文献
16.
The EPR and magnetic Mössbauer spectra of a series of axial ligand complexes of tetrakis(2,6-dimethoxyphenyl)porphyrinatoiron(III), [(2,6-(OMe)2)4TPPFeL2]+, where L=N-methylimidazole, 2-methylimidazole, or 4-(dimethylamino)pyridine, of one axial ligand complex of tetraphenylporphyrin, the bis(4-cyanopyridine) complex [TPPFe(4-CNPy)2]+, and of one axial ligand complex of tetraphenylchlorin, [TPCFe(ImH)2]+, where ImH=imidazole, have been investigated and compared to those of low-spin Fe(III) porphyrinates and ferriheme proteins reported in the literature. On the basis of this and previous complementary spectroscopic investigations, three types of complexes have been identified: those having (dxy)2(dxz,dyz)3
electronic ground states with axial ligands aligned in perpendicular planes (Type I), those having (dxy)2(dxz,dyz)3
electronic ground states with axial ligands aligned in parallel planes (Type II), and those having the novel (dxz,dyz)4(dxy)1
electronic ground state (Type III). A subset of the latter type, with planar axial ligands aligned parallel to each other or strong macrocycle asymmetry that yield rhombic EPR spectra, cannot be created using the porphyrinate ligand. Type I centers are characterized by "large
gmax" EPR spectra with g>3.2 and well-resolved, widely spread magnetic Mössbauer spectra having Azz/gNN>680 kG, with Axx negative in sign but much smaller in magnitude than
Azz, while Type II centers have well-resolved rhombic EPR spectra with gzz=2.4–3.1 and also less-resolved magnetic Mössbauer spectra, and usually have Azz/gNN
in the range of 440–660 kG (but in certain cases as small as 180 kG) and
Axx again negative in sign but only somewhat smaller (but occasionally larger in magnitude) than Azz, and Type III centers have axial EPR spectra with
g┴2.6 or smaller and g║<1.0–1.95, but often not resolved, and less-resolved magnetic Mössbauer spectra having
Azz/gNN
in the range of 270–400 kG, and
Axx again negative in sign but much smaller in magnitude than
Azz. An exception to this rule is [TPPFe(4-CNPy)2]+, which has
Axx/gNN=–565 kG, Ayy/gNN=629 kG, and Azz/gNN=4 kG. A subset of Type II complexes (Type II) have rhombicities (V/) much greater than 0.67 and Azz/gNN
ranging from 320 to 170 kG, with
Axx also negative but with the magnitude of
Axx significantly larger than that of
Azz. These classifications are also observed for a variety of ferriheme proteins, and they lead to linear correlations between
Azz
and either
Axx,
gzz, or V/ for Types I and II (but not for Azz versus V/ for Type II). Not enough data are yet available on Type III complexes to determine what, if any, correlations may be observed.Abbreviations CCP
cytochrome c
peroxidase
- 4-CNPy
4-cyanopyridine
- cyt
cytochrome
- EFG
electric field gradient
- ESEEM
electron spin echo envelope modulation
- ImH
imidazole
- Mb
myoglobin
- MCD
magnetic circular dichroism
- 2-MeImH
2-methylimidazole
- N-MeIm
N-methylimidazole
- 3NH2PzH
3-aminopyrazole
- 4-NMe2Py
4-(dimethylamino)pyridine
- [2,6-(OMe)2]4TPP
dianion of tetrakis(meso-2,6-dimethoxyphenyl)porphyrin
- OEiBC
dianion of octaethylisobacteriochlorin
- OEP
dianion of octaethylporphyrin
- PPIX
dianion of protoporphyrin IX
- Py
pyridine
- TMP
dianion of
meso-tetramesitylporphyrin
- TPC
dianion of
meso-tetraphenylchlorin
- TPP
dianion of
meso-tetraphenylporphyrin
- 2,6-XylylNC
2,6-xylyl isocyanide 相似文献
17.
Alexander G. Sobol Alexander S. Arseniev Galina V. Abdulaeva Larisa Yu. Musina Vladimir F. Bystrov 《Journal of biomolecular NMR》1992,2(2):161-171
Summary The conformation of chymotryptic fragment C2 of bacteriorhodopsin (residues 1–71) was studied by 2D1H NMR. The fragment was solubilized in a mixture of chloroform/methanol (11), 0.1 M LiClO4. Most of the resonances in1H NMR spectra of fragment C2 were assigned using phase-sensitive DQF-COSY, TOCSY, and NOESY techniques. To simplify the assignment procedure for overlapping regions of NMR spectra, an analog of fragment C2 with leucines deuterated in -positions was used. Deuterium exchange rates for amide protons were measured in a series of TOCSY spectra. Two right-handed -helical regions Pro8-Lys30 and Lys41-Leu62 were identified on the basis of NOE connectivities and deuterium exchange rates. The N-terminal part of the fragment (Ala.2-Gly6) adopts the helical conformation stabilized by 3 hydrogen bonds. 相似文献
18.
Subchronic treatment with MAP (4.6 mg/kg, i.p., once daily for 11 days) significantly decreased the Kd, but not Bmax, values of [3H]1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) binding to adenosine A1 receptors in the prefrontal cortex and hippocampus, but not striatum, of rat brain. However, subchronic treatment with PCP (10 mg/kg, i.p., once daily for 11 days) did not alter the Kd and Bmax values of [3H]DPCPX binding to adenosine A1 receptors in these three regions. Subchronic treatment with MAP or PCP did not alter the Bmax and Kd values of [3H]2-p-(2-carboxyehyl)phenethylamino-5-N-ethylcarboxyamidoadenosine ([3H]CGS21680) binding to adenosine A2A receptors in the striatum. Furthermore, subchronic treatment with MAP or PCP significantly decreased the specific binding of [3H]CGS21680 to adenosine A2A receptors in the hippocampus, but not in the prefrontal cortex. Thus, these results suggest that MAP and PCP may produce differential effects on the adenosine A2A receptors, but not adenosine A1 receptors in rat brain. 相似文献
19.
The FB iron-sulfur cluster is destroyed preferentially by treating Photosystem I complexes with HgCl2(Kojima Y, Niinomi Y, Tsuboi S, Hiyama T and Sakurai H (1987) Bot Mag 100: 243–53). When FB is 95% depleted but FAis quantitatively retained in cyanobacterial PS I complexes, the reduction potential of FA remains highly electronegative (Em=–530 mV, n=1), the EPR spectral and spin relaxation properties of FA and FXremain unchanged, but NADP+ photoreduction rates decline from 552 to 72 mol mg Chl–1 h–1.When FB is reconstituted with FeCl3, Na2S and -mercaptoethanol, NADP+photoreduction rates recover to 528 mol mg Chl–1 h–1. The correlation between the presence of FBand NADP+ photoreduction provides direct experimental evidence that this iron-sulfur cluster is required for electron throughput from cytochromec
6 to flavodoxin or ferredoxin in Photosystem I.Abbreviations Chl
chlorophyll
- DPIP
dichlorophenolindophenol
- PS I
Photosystem I
Published as Journal Series #11091 of the University of Nebraska Agricultural Research Division. This paper is dedicated to the memory of the late Professor Daniel Arnon, who is remembered for his gracious and generous encouragement of the senior author's early career. 相似文献
20.
Jaroniec CP Boisbouvier J Tworowska I Nikonowicz EP Bax A 《Journal of biomolecular NMR》2005,31(3):231-241
New 3D HCN quantitative J (QJ) pulse schemes are presented for the precise and accurate measurement of one-bond 15N1/9–13C1, 15N1/9–13C6/8, and 15N1/9–13C2/4 residual dipolar couplings (RDCs) in weakly aligned nucleic acids. The methods employ 1H–13C multiple quantum (MQ) coherence or TROSY-type pulse sequences for optimal resolution and sensitivity. RDCs are obtained from the intensity ratio of H1–C1–N1/9 (MQ-HCN-QJ) or H6/8–C6/8–N1/9 (TROSY-HCN-QJ) correlations in two interleaved 3D NMR spectra, with dephasing intervals of zero (reference spectrum) and 1/(2JNC) (attenuated spectrum). The different types of 15N–13C couplings can be obtained by using either the 3D MQ-HCN-QJ or TROSY-HCN-QJ pulse scheme, with the appropriate setting of the duration of the constant-time 15N evolution period and the offset of two frequency-selective 13C pulses. The methods are demonstrated for a uniformly 13C, 15N-enriched 24-nucleotide stem-loop RNA sequence, helix-35, aligned in the magnetic field using phage Pf1. For measurements of RDCs systematic errors are found to be negligible, and experiments performed on a 1.5 mM helix-35 sample result in an estimated precision of ca. 0.07 Hz for 1DNC, indicating the utility of the measured RDCs in structure validation and refinement. Indeed, for a complete set of 15N1/9–13C1, 15N1/9–13C6/8, and 15N1/9–13C2/4 dipolar couplings obtained for the stem nucleotides, the measured RDCs are in excellent agreement with those predicted for an NMR structure of helix-35, refined using independently measured observables, including 13C–1H, 13C–13C and 1H–1H dipolar couplings.Supplementary material to this paper is available in electronic form at
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