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At least 649 records · Page 36Linked to original sources
PubMed2004

[Study on the spectrum response characteristic based on the wide type bacteriorhodopsin film].

The photochromic retinal protein bacteriorhodopsin (BR) was found in the cell membrane of the Archaean Halobacterium salinarium. The excellent photochromic and photocycle properties of the BR provide the possibility of many applications in the filed of optical information processing. In this paper, the spectrum response characteristic of the wild type bacteriorhodopsin molecule film was studied by using pump-probe method. After the samples was excited by 532 nm YAG laser beam, the absorption spectra were probed by an optical fiber spectrum analysis (OSA). The absorption peaks at the ground state (B state) of the two samples are all at 562 nm wavelength. At 562 nm wavelength, the optical densities (OD) of the samples are about OD (WT1) 562 nm = 2.04 and OD (WT2) 562 nm = 1.37 respectively. The experiment results show that BR(WT) films have absorption that appears to strengthen with the probe time increasing in wavelength 550-650 nm, and this change phenomenon is described by spectra measured at different probe time. Appling the theoretical plot-fit of two exponentials to analyze the process of the absorption change it is found that this change includes two processes-fast process and slow process. Their corresponse time constants of BR(WT1) are about 11 ms and 60 s, and those of BR(WT2) about 24 and 30 s respectively.

Absorption↗
PubMed2002

[Using purified conjugated bilirubin as a calibrator for bilirubin measurement].

OBJECTIVES: To improve the accuracy and precision of the determination of bilirubin, especially direct bilirubin (DB), and the standardization of that as well. METHODS: Purified conjugated bilirubin (Bc) and ditaurobilirubin(DTB) and their diazo products were subjected to absorption spectrum analysis. The diazo reaction characters of their calibration solutions were compared by the method of Doumas J-G(TB & DB). RESULTS: Bc, DTB and their azopigments were found to have the similar absorption spectra with the same lambda max. Their TB standard curves almost superposed together all over. Although the slopes of their DB standard curves were not markedly different ((YBc = 0.00366X + 0.00933, rBc2 = 0.9977, P < 0.01; YDTB = 0.00391X + 0.00023, rDTB2 = 0.9987, P < 0.01; Pb1-b2 > 0.05, n1 = n2 = 5), the DB value measured for Bc differed from that for DTB(n = 5, P < 0.05). In addition, the calibrators made from Bc based different matrices, such as HSA, BSA and human serum, were significantly different in DB/Bc, but no difference was seen among the concentrations. Furthermore, the DB values determined for DTB or Bc increased linearly with the corresponding concentrations, respectively, with no difference between the slopes (YBc = 0.8300XBc + 1.9463, rBc2 = 0.9977, P < 0.01; YDTB = 0.8853XDTB-0.0251, rDTB2 = 0.9986, P < 0.01; n1 = n2 = 5, Pb1-b2 > 0.05). CONCLUSIONS: The results demonstrate that the diazo reaction characters of Bc are identified with those of DTB. However, under the condition of DB, Bc reacts differently from DTB. This study also indicates that as a calibrator of DB based human serum, Bc has the similar constant effect of HCl as serum samples do, so it is a more reliable calibrator to eliminate the matrix effects.

Bilirubin↗
PubMed2001

Physiological tremor of the upper limb segments.

The acceleration signal produced by physiological tremor from four different upper limb segments (the finger, hand, forearm and upper limb) was measured by an acceleration sensor during holding posture and was analyzed by power spectrum analysis. Two prominent peaks appeared in the power spectrum, suggesting that the tremor in the four different limb segments was composed of two frequency components. The frequency of one peak at 8-12 Hz did not change between the different limb segments, while the frequency of the other peak decreased with the increase in the mass of the limb segment. A model with two reflex pathways was developed for the tremor in the four limb segments. The model includes two reflex pathways, a spinal pathway and a supraspinal pathway. The theoretical values of the frequency and the amplitude of the tremor predicted by the model were in good agreement with the experimental results. Analysis of the model revealed that one of the two frequency components of the tremor was of spinal origin and was dependent upon the mass of the limb segment, and the second was of supraspinal origin, corresponding to the frequency at 8-12 Hz. In the normal subject, it is possible that the tremor could be used to evaluate the change in neuromuscular function produced by prolonged work involving just part of a limb segments (e.g., typing). It may also be used to evaluate the neuromuscular function of patients suffering from neurological diseases such as muscular dystrophy and Parkinson's disease.

Adult↗
PubMed1998

Understanding heme cavity structure of peroxidases: comparison of electronic absorption and resonance Raman spectra with crystallographic results.

Electronic absorption and resonance Raman spectra of various peroxidases and selected site-directed mutants are reported. These results and the X-ray crystal structure data are critically analyzed and underline the differences that exist between the crystal and solution states. The effect of the vinyl conjugation on the electronic absorption maxima and the influence of the ligand nature on the wavelength of the charge-transfer (CT1) band are shown to be useful probes of subtle interactions in the heme pocket. The spectroscopic differences observed between the three classes of peroxidases are discussed in terms of their structural diversity.

Binding Sites↗
PubMed2000

Interactions of phosphatidylinositol 3-kinase Src homology 3 domain with its ligand peptide studied by absorption, circular dichroism, and UV resonance raman spectroscopies.

Absorption, circular dichroism (CD), and UV resonance Raman (UVRR) spectroscopies were applied to selectively examine the environmental and structural changes of Trp and Tyr residues in the phosphatidylinositol 3-kinase (PI3K) SH3 domain induced by ligand association. Comparison of the spectra of PI3K SH3 in the presence or absence of its ligand peptide RLP1 (RKLPPRPSK) indicated that RLP1 binding changed the environment of Trp55 of the SH3 to be more hydrophilic and its H bonding weaker and that of Tyr residues to be more hydrophobic. The D21N mutant (Asp21 --> Asn) of the SH3 yielded a UV CD distinct from that of the wild type, and its spectral changes induced by RLP1 binding were smaller and different from those of the wild type in absorption, CD, and UVRR spectra, suggesting that the mutation of conserved Asp21 affected the conformation of the ligand binding cleft and thus might lead to the decrease in the ligand affinity. These data provide direct evidence for the occurrence of environmental and structural changes of PI3K SH3 by the association of a ligand and the D21N mutation.

Absorption↗
PubMedDate not supplied

Time-resolved spectroscopic fluorescence imaging, transient absorption and vibrational spectroscopy of intact and photo-inhibited photosynthetic tissue.

Fluorescence, absorption and vibrational spectroscopic techniques were used to study spinach at the photosystem II (PS II), chloroplast and cellular levels and to determine the effects and mechanisms of ultraviolet-B (UV-B) photoinhibition of these structures. Two-photon fluorescence spectroscopic imaging of intact chloroplasts shows significant spatial variations in the component fluorescence spectra in the range 640-740 nm, indicating that the type and distribution of chlorophylls vary markedly with position in the chloroplast. The chlorophyll distributions and excitonic behaviour in chloroplasts and whole plant tissue were studied using picosecond time-gated fluorescence imaging, which also showed UV-induced kinetic changes that clearly indicate that UV-B induces both structural and excitonic uncoupling of chlorophylls within the light-harvesting complexes. Transient absorption measurements and low-frequency infrared and Raman spectroscopy show that the predominant sites of UV-B damage in PS II are at the oxygen-evolving centre (OEC) itself, as well as at specific locations near the OEC-binding sites.

Chlorophyll↗
PubMed2006

Secondary conformation of short lysine- and leucine-rich peptides assessed by optical spectroscopies: effect of chain length, concentration, solvent, and time.

Solution secondary structures of three synthetic cationic peptides, currently used in antisense oligonucleotide delivery into living cells, have been analyzed by means of circular dichroism (CD) and Raman scattering in different buffers as a function of concentration and time. All three peptides are of minimalist conception, i.e., formed by only two types of amino acids (leucine: L and lysine: K). Two of these peptides contain 15 aminoacids: N(ter)- KLLKLLLKLLLKLLK (L(10)K(5)), N(ter)-KLKLKLKLKLKLKLK (L(7)K(8)), and the third one has only 9 residues: N(ter)-KLKLKLKLK (L(4)K(5)). The conformational behavior of the 15-mers in pure water differs considerably one from another. Although both of them are initially disordered in the 50-350 microM range, L(10)K(5) gradually undergoes a disordered to alpha-helix transition for molecular concentrations above 100 microM. In all other solvents used, L(10)K(5) adopts a stable alpha-helical conformation. In methanol and methanol/Tris mixture, nonnative alpha-helices can be induced in both KL-alternating peptides, i.e., L(7)K(8) and L(4)K(5). However, in major cases and with a time delay depending on peptide concentration, beta-like structures can be gradually formed in both solutions. In PBS and methanol/PBS mixture, the tendency for L(7)K(8) and L(4)K(5) is to form structures belonging to beta-family. A discussion has been undertaken on the effect of counterions as well as their nature in the stabilization of ordered structures in both KL-alternating peptides.

Amino Acid Sequence↗
PubMed2005

Nonlinear optical spectroscopy of chiral molecules.

We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest.

Circular Dichroism↗
PubMed2005

Coherent control for spectroscopy and manipulation of biological dynamics.

Motivated originally by the goal of steering a photoreaction into desired product channels, the concept of coherent control is to adapt the spectral and temporal characteristics of the excitation light to the inherent molecular resonances and dynamics, such that these can be selectively addressed and manipulated. In the last decade, the ultrafast dynamics of many atomic and molecular quantum systems in the gas and condensed phase have been controlled successfully. Motivations in chemistry are now 1) to perform spectroscopy by coherent control, which requires a deeper understanding of control mechanisms, 2) to treat more complex, biological photoreactions, and 3) the pragmatic use of coherent control techniques, for example, for pulse compression or enhanced contrast in multiphoton microscopy. As examples for 1) and 2) we review here the combined effort and interplay of conventional spectroscopy and coherent control experiments, applied to the energy flow in the light-harvesting complex LH2 from bacterial photosynthesis. Closed-loop control experiments allowed the characteristic coupling frequency of internal conversion in the carotenoid in LH2 to be extracted. Open-loop three-pulse control experiments, on the other hand, could directly observe an anticipated Raman-excited carotenoid ground state. As a variant of difference spectroscopy, coherent control has thus served to gain complementary spectroscopic knowledge about the energy flow in carotenoids by comparing natural to manipulated dynamics. Finally, we propose future coherent control experiments on the electronic state structure of carotenoids and discuss prospects of coherent control for other biological chromophores.

Biophysics↗
PubMed1994

Characterization of flavocytochrome C552 from the thermophilic photosynthetic bacterium Chromatium tepidum.

A M(r) 68 kDa flavocytochrome c552 has been isolated from the thermophilic photosynthetic purple sulfur bacterium Chromatium tepidum and shown to consist of a M(r) 25 kDa subunit that contains two covalently bound heme c and a M(r) 43 kDa subunit that probably contains a single FAD. The prosthetic group content, absorbance spectra, and subunit composition of the C. tepidum flavocytochrome are quite similar to those previously reported for the flavocytochrome c552 isolated from a mesophilic Chromatium species, Chromatium vinosum. The oxidation-reduction properties of the hemes present in the C. tepidum flavocytochrome have been characterized by titrations, the effect of temperature on the catalytic activity of the protein has been investigated, and the heme environment has been characterized using resonance Raman spectroscopy.

Chromatium↗
PubMed1998

Structural and functional roles of heme binding module in globin proteins: identification of the segment regulating the heme binding structure.

To investigate structural and functional significance of a newly proposed structural unit in globins, the "heme binding module", we synthesized a "heme binding module"-substituted chimeric globin and characterized its function and structure. In our previous study we proposed that the heme binding module, corresponding to the segment from Leu(F1) to Phe(G5) in hemoglobin alpha-subunit, plays a key role in constructing the heme proximal structure in globins. The replacement of the heme binding module in myoglobin with that of hemoglobin alpha-subunit converted the absorption spectra into that of the alpha-subunit, and, in the resonance Raman spectra, the vibration mode characteristic of myoglobin completely disappeared after the module replacement. The hyperfine-shifted NMR resonances for the cyanide-bound form of the module-substituted myoglobin also revealed that the orientation of the axial histidine is close to that of the alpha-subunit rather than that of myoglobin, while the deviations of the resonance positions of the NMR signals from the amino acid residues located in the distal site were subtle, supporting the preferential structural alterations in the heme proximal site. The present finding for the structural alterations in the module-substituted myoglobin confirms that the heme binding module can be a segment regulating the heme proximal structure in globin proteins.

Amino Acid Sequence↗
PubMed1958

Microphotometry.

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Spectrum Analysis↗
PubMed2003

Spectroscopic characterization of natural corals.

The FTIR, micro-Raman, NMR, and XPS spectra of 25 different natural corals have been compared. Reflectance and transmission absorbance IR and Raman data have been used as rapid and efficient means of classification of natural corals containing aragonite (non-precious white species), calcite (red, pink, precious white species), and organic material (black protein polymer). The combination of reflectance IR and infrared microscopy could serve as a rapid, non-destructive method for distinguishing natural corals from artificial, fake jewels.

Animals↗
PubMed2000

Saccharose solid matrix embedded proteins: a new method for sample preparation for X-ray absorption spectroscopy.

In this study, solid samples of hemoglobin and hemocyanin have been prepared by embedding the proteins into a saccharose-based matrix. These materials have been developed specifically for specimens for X-ray absorption spectroscopy (XAS). The preservation of protein conformation and active site organization was tested, making comparisons between the solid and the corresponding liquid samples, using resonance Raman, infra red, fluorescence and XAS. The XAS spectra of irradiated solid and liquid samples were then compared, and the preservation of biological activity of the proteins during both preparation procedure and X-ray irradiation was assessed. In all cases, the measurements clearly demonstrate that protein solid samples are both structurally and functionally quite well preserved, much better than those in the liquid state. The saccharose matrix provides an excellent protection against X-ray damages, allowing for longer exposure to the X-ray beam. Moreover, the demonstrated long-term stability of samples permits their preparation and storage in optimal conditions, allowing for the repetition of data collection with the same sample in several experimental sessions. The very high protein concentration that can be reached results in a significantly better signal-to-noise ratio, particularly useful for high molecular weight proteins with a low metal-to-protein ratio. On the bases of the above-mentioned results, we propose the new method as a standard procedure for the preparation of biological samples to be used for XAS spectroscopy.

Animals↗