共查询到20条相似文献,搜索用时 10 毫秒
1.
2.
C_(20)-二萜生物碱结构复杂,环上大多有含氧的基团。利用NMR、MS等确定羟基、羰基在分子中的位置往往不够有力。特別是对于C_1~3或C_(11)位上羰基,没有可靠而简便的光谱鉴別方法。我们通过对几个Atisine型含羰基化合物的圆二色谱研究发现,由CD谱确定羰基在C_6位、C_(11)位及C_(13)位是一种简便有效的方法。 相似文献
3.
Abstract— The magnetic circular dichroism (MCD) (300–850nm) of the bacteriochlorophyll (Bchl) a -protein from the green photosynthetic bacterium Prosthecochloris aestuarii 2 K is qualitatively similar to the MCD of Bchl a in methanol and ether solution. This result implies that the transition dipole of the lowest energy electronic transition (near 800 nm) is roughly perpendicular to the transition dipole of the next higher electronic band (near 600nm) for Bchl a molecules in the protein just as it is for molecules in solution. This result provides no support for the recent proposal that interactions with the protein rotates the direction of the transition dipoles of the 800nm band of all the Bchl a molecules in the protein by 90°. While a rotation of the 800nm transition dipoles cannot be rigorously excluded, it would be necessary for the postulated perturbation to rotate the transition dipoles of both the 800 and 600nm bands by 90°. In a broader sense, any postulated perturbation would have to be shown to leave both the absorption spectrum and the MCD largely unaffected. MCD is a more sensitive test than absorption spectroscopy for perturbations of electronic states and changes in the relative orientation of transitions, because it depends on both the magnitudes and directions of at least two electric and one magnetic transition dipole. 相似文献
4.
Gudrun Hermann Max E. Lippitsch Harald Brunner Franz R. Aussenegg Eberhard Müller 《Photochemistry and photobiology》1990,52(1):13-18
Abstract— A comparative study of the picosecond kinetics of rye ( Secale cereale L.) phytochrome, its 39 and 23 kDa chromopeptides and deuterated rye phytochrome has been carried out. Evidence is presented that the fluorescence decay of Pr contains a very short lifetime component (14 ps) which has escaped detection in the fluorescence studies reported so far. Thus, the overall decay is well described by four exponential components, two rapid (14 and 44 ps) and two slower ones (157 and 690 ps). The fluorescence decays of deuterated Pr and of a 39 and 23 kDa chromopeptide of Pr also require the analysis in terms of four exponentials for a good fit. Some of the lifetime and amplitude values obtained differ significantly from the values estimated for Pr. In the chromopeptides, the two longer components have distinctly slower decays. For the two faster components the lifetimes remain approximately the same, but their relative amplitudes vary greatly. In deuterated Pr, the lifetimes are affected only slightly by deuteration. In contrast, the decay amplitudes are strikingly altered. Moreover, from a rate equation simulation modelling the observed fluorescence kinetics, it turns out that the yields for the various deactivation steps in the chromopeptides and in deuterated Pr reveal differences from the corresponding values in Pr. The implications of the results presented with respect to the influence of the protein moiety of Pr on the picosecond relaxation process are discussed. 相似文献
5.
Abstract— The near UV and visible circular dichroism (CD) spectra of rhodopsin solubilized and purified in sodium cholate have been determined. The CD properties of rhodopsin in 2 and 20mg/ml sodium cholate are substantially different in terms of the α band to β band ratio, and sensitivity of the near UV CD spectra to bleaching. Rhodopsin in 2mg/m l sodium cholate will regenerate (11- cis -retinal + opsin → rhodopsin) and has a CD spectrum similar to rhodopsin in rod outer segment membranes and digitonin which will also regenerate. On the other hand rhodopsin in 20mg/m l sodium cholate will not regenerate and has CD properties similar to other nonregenerable detergents (cetyltri-methylammonium salts and emulphogene). These results indicate that CD reflects the conformational integrity of functional (regenerable) rhodopsin and that sodium cholate can reversibly alter the conformation of rhodopsin. Finally the results further support the validity of using sodium cholate solubilized rhodopsin as a model system for studies on the structure and function of rhodopsin. 相似文献
6.
CIRCULAR DICHROISM OF BOVINE RHODOPSIN 总被引:2,自引:0,他引:2
HITOSHI SHICHI 《Photochemistry and photobiology》1971,13(6):499-502
Abstract— When rhodopsin is associated with membrane particles, phospholipid may be involved in maintaining a preferred conformation of the opsin and the asymmetric structure of the chromophore of rhodopsin. 相似文献
7.
Abstract— The in vivo photostationary state, φfr = ([ P fr ]fr /[ P ]), of phytochrome in far red light has been determined in mustard seedling cotyledons by three different methods. The φfr is a function of the length of time of etiolation ( t = 36 hr, φfr = 0·14; t = 72 – 120 hr, φfr = 0·075). The calculated φr = 0·8. The amount of P tot is strongly dependent on the time of onset of far red light. These data imply that it would be almost impossible to maintain a constant level of P fr in mustard cotyledons over a considerable period of time. 相似文献
8.
P. S. Maruthi Sai S. Siebzehnrübl S. Mahajan H. SCHEER† 《Photochemistry and photobiology》1993,57(1):71-75
Two phycoerythrocyanin (PEC) fractions have been obtained from the phycobilisomes of the cyanobac-terium Westiellopsis prolifica ARM 365. They have been characterized by absorption, fluorescence and circular dichroism spectroscopy. One of them is spectroscopically similar to a PEC trimer known from other organisms. Whereas efficient energy transfer from its violin (α-84) to the cyanin (β-84, 155) chromophores is efficient in the trimer (αβ it is impeded after dissociation to the monomer (α,β). A second fraction of PEC which we earlier termed PEC(X) (Maruthi Sai et al., Photochem. Photobiol. 55 ,119–124, 1992), exhibited the spectral properties similar to that of the α-subunit of PEC from Mastigocladus laminosus. With this highly photoactive fraction, the circular dichroism spectra of the violobilin chromophore in both photoreversible states were obtained. 相似文献
9.
用圆二色谱研究温度对海藻酸钠中生物功能微区的影响 总被引:1,自引:0,他引:1
通过4个不同组成的海藻酸钠样品圆二色CD信号随温度变化的谱图,结合X-射线衍射、13C-NMR技术,证明海藻酸钠中存在双螺旋结构的生物功能微区.通过4个样品的对比说明G段单元是形成双螺旋结构的物质基础;G段形成双螺旋生物功能微区结构,随温度变化发生有序-无序可逆转变的过程,与晶体随温度"融化"和"成核"过程相似. 相似文献
10.
Thierry Brotin Jacek Waluk Jean-Pierre Desvergne Henri Bouas-Laurent Josef Michl 《Photochemistry and photobiology》1992,55(3):335-347
Abstract— Linear dichroism (LD) and magnetic circular dichroism (MCD) of symmetrical dialkoxy-anthracenes and some related compounds were recorded in an attempt to elucidate electronic absorption properties and assign the nature of the lowest singlet excited state, recognized to control both the fluorescence and the photodimerization of anthracenes. The spectroscopic measurements proved that the lowest electronic transition is of the 1La type in all the compounds. The peculiar photoreactivity pattern is therefore governed by factors other than an inversion of the order of the 1La and 1Lb states and may be related to electronic density repartition on the different positions of the anthracene nucleus dictated by the position of the electron-donating substituents. 相似文献
11.
12.
采用圆二色谱方法对钕和镧离子与转移核糖核酸间的相互作用进行了研究,结果显示在1.5~6 μmol/L Nd3+或La3+离子存在下,tRNA分子CD谱260 nm(+)峰蓝移2~3 nm, 260 nm(+)峰值分别增加6%和20%左右;210 nm(-)峰在不同摩尔比Nd3+/tRNA作用下,谱峰蓝移或红移,峰值增加或降低50%左右。结果说明结合在tRNA分子上的Nd3+或La3+可能引起tRNA分子构象的变化。Eu3+对大肠杆菌LeuRS或tRNALeu-LeuRS复合物的CD谱具有一定的影响。 相似文献
13.
A SIMPLE AND IMPROVED METHOD OF ISOLATION AND PURIFICATION FOR NATIVE OAT PHYTOCHROME 总被引:2,自引:0,他引:2
Abstract— A simple procedure for the isolation and purification of 124 kDa phytochrome (phyA) from etiolated Avena seedlings has been developed employing ammonium sulfate back-extraction. After solubilization of the ammonium sulfate precipitate (250 g/L) an additional ammonium sulfate fractionation with 17 g per 100 mL rather than column chromatography was performed. After several steps of the "washing-out" procedure with 100 mM phosphate buffer, phytochrome was solubilized in 10 m M phosphate buffer. The resulting phytochrome had a specific absorbance ratio (SAR = A666 /A28 o) ranging from 0.60 to 0.85. These values are equivalent to those of phytochrome preparations after hydroxyla-patite chromatography-ammonium sulfate back-extraction. The total isolation-purification time was 8 h and yield of the chromoprotein was 50% higher than the yield using conventional techniques. The phytochrome preparation, after application to a Toyopearl HW-65S gel filtration column, produced very pure 124 kDa phyA with a specific absorbance ratio greater than 1.00. The spectral characteristics are identical to those described for the best of the highly purified native chromoprotein preparations. 相似文献
14.
THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—III. MEASUREMENT AND CALCULATION OF PHYTOCHROME PHOTOEQUILIBRIA 总被引:1,自引:0,他引:1
Abstract— Phytochrome photoequilibria have been measured in dark-grown Phaseolus uulgaris L . and Cucurbita pepo I . hypocotyl hooks which had been exposed to various natural and artificial radiation sources. Mean phytochrome photoequilibria ( φ ) varied from 0.20 within a wheat canopy to 0.54 above, although lower values were occasionally observed in densely shaded areas. Greater variation in phyto chrome photoequilibria and lower levels of Pfr were recorded within a sugar beet canopy. The range of photoequilibria was φ= 0.04 in dense shade to φ= 0.54 above the canopy. Photoequilibrium was achieved within 5 s in mid-day sunlight and approximately 30 s in dense canopy shade.
A close correlation was found between φ and the ratio of the quantum flux in the red and far-red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.
The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants. 相似文献
A close correlation was found between φ and the ratio of the quantum flux in the red and far-red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.
The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants. 相似文献
15.
John D. Bolt† C. Neil Hunter‡§ Robert A. Niederman‡ Kenneth Sauer 《Photochemistry and photobiology》1981,34(5):653-656
Abstract— The orientation of the chromophores in the B875 light-harvesting bacteriochlorophyll complex isolated from Rhodopseudomonas sphaeroides by lithium dodecyl sulfate/polyacrylamide gel electrophoresis was examined by linear and circular dichroism and fluorescence polarization procedures. The circular dichroism in the near-IR was weaker than that of the B800–850 light-harvesting complex and had a distinctly different shape. This suggested a different geometry for the two bacteriochlorophylls of B875 and less interactive association between their transition moments. The magnitude of the circular dichroism in the carotenoid region of B875 was similar to that of B800–850 but gave more negative values between approx. 430–485 nm; this may reflect a difference in the asymmetric binding of carotenoids to the B875 protein. The fluorescence polarization increased sharply across the near-IR region of B875 and achieved very high values at long wavelengths. This confirmed that more than one transition contributed to this absorption band. The linear dichroism of B875 did not show a significant change in this near-IR band like that observed for the longest wavelength band of B800–850. Thus, the transition moments for each bacteriochlorophyll within B875 appear to be tilted to approximately the same extent with respect to the protein axis. These results distinguish B875 from all other light-harvesting complexes and suggest that the antennae of Rhodospirillaceae which contain a single near-IR absorption band cannot be classified into a single group. 相似文献
16.
17.
18.
Abstract— The phosphorescent triplet state of tryptophan has been studied by the method of optically detected magnetic resonance (ODMR) at pumped helium temperatures in zero magnetic field. Only one of the triplet sublevels is found to be significantly radiative; the other two decay radiationlessly. Although the phosphorescence and ODMR decay lifetimes are influenced by spin–lattice relaxation processes at T = 1.3°K, the lifetime of the radiative level can be estimated as approximately 2 s, whereas the lifetimes of the non–radiative levels are in excess of 10 s. Comparison of the ODMR signals and the phosphorescence spectra has been made for tryptophans in native proteins with the following results: the ODMR signals of the two types of tryptophan sites in horse liver alcohol dehydrogenase can be resolved due to a shift in the D and E values of the respective triplet states; binding of the substrate tri- N -acetylglucosamine to hen lysozyme leads to a considerable narrowing of the phosphorescence peaks and ODMR signals as well as to a shift in the E value of the triplet state.
The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The | E | value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line–broadening process which at present is not understood. 相似文献
The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The | E | value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line–broadening process which at present is not understood. 相似文献
19.
T. Lamparter P. Lutterbüse H. A. W. Schneider-Poetsch R. Hertel 《Photochemistry and photobiology》1992,56(5):697-707
We confirmed that after extraction in the absence of added Mg2+, a small fraction of phytochrome was associated with pelletable, hydrophobic membranes. When microsomal material of several plant species was subjected to Triton X-114 phase partitioning, a part of phytochrome migrated into the hydrophobic Triton phase in contrast to soluble phytochrome. The amount of bound phytochrome partitioning into the Triton phase varied from 6% for oats to 30% for zucchini and 50% for mustard and maize (0.5–10% of total phytochrome). Membrane-associated phytochrome could be solubilized by the zwitterionic detergent CHAPS and with the nonionic detergent dodecylmaltoside. Subjected to gel filtration on Superose-6/FPLC, oat phytochrome of the CHAPS solubilized sample was eluted in three different molecular weight ranges. There was a main fraction with the molecular weight of purified phytochrome, another fraction (approximately 20%) with a higher molecular weight, and a third small fraction appearing immediately after the void volume. Gel filtration after solubilization by dodecylmaltoside resulted in two distinct fractions: the one eluted at the position of the phytochrome dimer, and the other (approximately 15%) with an apparent molecular weight of 800 kDa. Phytochrome was detected, separated and quantified by SDS-PAGE, and western blotting with the monoclonal antibody Z-3B1. We assume that the distinct, phytochrome positive, high molecular weight fractions contain phytochrome associated with hydrophobic protein. 相似文献
20.
EXTENDING CIRCULAR DICHROISM SPECTRA INTO THE VACUUM UV AND ITS APPLICATION TO PROTEINS 总被引:1,自引:0,他引:1
Circular dichroism (CD) spectra measured into the vacuum UV region provide information necessary for this technique to fulfill its potential. In the case of proteins, CD spectra measured to 184 nm or below can be analyzed for secondary structure: generalized inverses make such analyses particularly simple. Generalized inverses for α-helix, anti-parallel β-sheet, parallel β-sheet, β-turn, and "other" structures are given in tabular form. When the dot product of each inverse is taken with the digitized spectrum of a protein, the amount of corresponding secondary structure is predicted. However, protein CD spectra truncated above 184 nm give too little information to give reliable analyses. Furthermore, adding constraints only complicates this problem because unreliable analyses now appear good. 相似文献