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A Gall

Publications and source records attributed to A Gall.

15 recordsLinked to original sources
PubMed2001

Probing the binding sites of exchanged chlorophyll a in LH2 by Raman and site-selection fluorescence spectroscopies.

In this work we have selectively released the 800 nm absorbing bacteriochlorophyll a molecules of the LH2 protein from the photosynthetic bacterium Rhodopseudomonas acidophila, strain 10050, and replaced them with chlorophyll a (Chla). A combination of low-temperature electronic absorption, resonance Raman and site-selection fluorescence spectroscopies revealed that the Chla pigments are indeed bound in the B800 binding site; this is the first work that formally proves that such non-native chlorins can be inserted correctly into LH2.

Bacterial Proteins↗
PubMed2001

Effect of high pressure on the photochemical reaction center from Rhodobacter sphaeroides R26.1.

High-pressure studies on the photochemical reaction center from the photosynthetic bacterium Rhodobacter sphaeroides, strain R26.1, shows that, up to 0.6 GPa, this carotenoid-less membrane protein does not loose its three-dimensional structure at room temperature. However, as evidenced by Fourier-transform preresonance Raman and electronic absorption spectra, between the atmospheric pressure and 0.2 GPa, the structure of the bacterial reaction center experiences a number of local reorganizations in the binding site of the primary electron donor. Above that value, the apparent compressibility of this membrane protein is inhomogeneous, being most noticeable in proximity to the bacteriopheophytin molecules. In this elevated pressure range, no more structural reorganization of the primary electron donor binding site can be observed. However, its electronic structure becomes dramatically perturbed, and the oscillator strength of its Q(y) electronic transition drops by nearly one order of magnitude. This effect is likely due to very small, pressure-induced changes in its dimeric structure.

Bacteriochlorophylls↗
PubMed2001

Post stroke depression.

Depression following stroke is common. Although it is highlighted as an issue in stroke guidelines, guidance on diagnosis or management is not given. This paper presents the original research from a literature review of Medline and the Cochrane Database on stroke and depression, and discusses some of the clinical implications of the findings.

Antidepressive Agents↗
PubMed1999

Conformation of bacteriochlorophyll molecules in photosynthetic proteins from purple bacteria.

Fourier transform near-infrared resonance Raman spectroscopy can be used to obtain information on the bacteriochlorophyll a (BChl a) molecules responsible for the redmost absorption band in photosynthetic complexes from purple bacteria. This technique is able to distinguish distortions of the bacteriochlorin macrocycle as small as 0.02 A, and a systematic analysis of those vibrational modes sensitive to BChl a macrocycle conformational changes was recently published [Näveke et al. (1997) J. Raman Spectrosc. 28, 599-604]. The conformation of the two BChl a molecules constituting the primary electron donor in bacterial reaction centers, and of the 850 and 880 nm-absorbing BChl a molecules in the light-harvesting LH2 and LH1 proteins, has been investigated using this technique. From this study it can be concluded that both BChl a molecules of the primary electron donor in the photochemical reaction center are in a conformation close to the relaxed conformation observed for pentacoordinate BChl a in diethyl ether. In contrast, the BChl a molecules responsible for the long-wavelength absorption transition in both LH1 and LH2 antenna complexes are considerably distorted, and furthermore there are noticeable differences between the conformations of the BChl molecules bound to the alpha- and beta-apoproteins. The molecular conformations of the pigments are very similar in all the antenna complexes investigated.

Bacterial Proteins↗
PubMed1999

Bacteriochlorin-protein interactions in native B800-B850, B800 deficient and B800-Bchla(p)-reconstituted complexes from Rhodopseudomonas acidophila, strain 10050.

Recently, a method which allows the selective release and removal of the 800 nm absorbing bacteriochlorophyll a (B800) molecules from the LH2 complex of Rhodopseudomonas acidophila strain 10050 has been described [Fraser, N.J. (1999) Ph.D. Thesis, University of Glasgow, UK]. This procedure also allows the reconstitution of empty binding sites with the native pigment Bchla(p), esterified with phytol. We have investigated the bacteriochlorophylla-protein interactions in native, B800 deficient (or B850) and in B8110-bacteriochlorophylla(p)-reconstituted LH2 complexes by resonance Raman spectroscopy. We present the first direct structural evidence which shows that the reconstituted pigments are correctly bound within their binding pockets.

Bacterial Proteins↗
PubMed1999

Characterization of the different peripheral light-harvesting complexes from high- and low-light grown cells from Rhodopseudomonas palustris.

In this paper we demonstrate that the spectroscopically different peripheral light-harvesting complexes from Rhodopseudomonas palustris, strain 2.6.1, isolated from high- and low-light grown cells have widely differing bacteriochlorophyll a (BChl a) resonance Raman spectra in the high-frequency carbonyl region (1550-1750 cm-1). Complexes synthesized in low-light grown cells exhibit Raman spectra characteristic of B800-850 and B800-820 complexes, depending on the excitation conditions. The in vivo strategy for low-light adaptation in this bacterium is thus somewhat different from that generally encountered in the Rhodospirillaceae. In these bacteria, as typified by Rps. acidophila and Rps. cryptolactis, low-light conditions induce the synthesis of B800-820 only complexes in which the hydrogen bonds between the acetyl carbonyl and the B850 binding pocket are broken, inducing changes in the absorption properties of the monomeric bacteriochlorophylls. In the case of Rps. palustris, additional spectral effects occur due to the coupling of the electronic levels of the differently interacting dimers. The extensive use of differential alpha/beta-polypeptide expression [Tadros et al. (1993) Eur. J. Biochem. 217, 867-875] thus allows Rps. palustris to alter its BChl a binding site environments causing the observed spread of BChl a Qy transitions, ranging from 801 to 856 nm.

Bacteriochlorophylls↗
PubMed1999

Certain species of the Proteobacteria possess unusual bacteriochlorophyll a environments in their light-harvesting proteins.

In this work, we have examined, using Fourier-transform Raman (FT-R) spectroscopy, the bacteriochlorophyll a (BChl a) binding sites in light-harvesting (LH) antennae from different species of the Proteobacteria that exhibit unusal absorption properties. While the LH1 complexes from Erythromicrobium (E.) ramosum (RC-B871) and Rhodospirillum centenum (B875) present classic FT-R spectra in the carbonyl high-frequency region, we show that in the blue-shifted LH1 complex, absorbing at 856 nm, from Roseococcus thiosulfatophilus, as well as in the B798-832 LH2 from E. ramosum, or in the B830 complex from the obligate phototrophic bacterium Chromatium purpuratum, some H-bonds between the acetyl carbonyl of the BChl a and the surrounding protein are missing. The molecular mechanisms responsible for the unusual absorption of these complexes are thus similar to those responsible for tuning of the absorption of the LH2 complexes between 850 and 820 nm. Furthermore, our results suggest that the binding pocket of the monomeric BChl in the LH2 from E. ramosum is different from that of Rps. acidphila or Rb. sphaeroides. The FT-R spectra of Chromatium purpuratum indicate that, in contrast with every LH2 complex previously studied by FT-R spectroscopy, no free-from-interaction keto groupings exist in this complex.

Bacteriochlorophylls↗
PubMed1998

The effect of pressure on the bacteriochlorophyll a binding sites of the core antenna complex from Rhodospirillum rubrum.

In this paper we examine the effect of pressure on the absorption spectrum and binding site of the core antenna complex from the photosynthetic bacterium Rhodospirillum rubrum. Absorption spectra and Raman spectra in preresonance with the Qy transition of the bacteriochlorophyll a were studied at pressures up to 625 MPa. In agreement with previous work we observe a pressure-induced red shift and broadening of the absorption spectrum. We show that at these pressures the pigments within the protein matrix at room temperature experience little if any distortion, and the hydrogen-bonding network involving the C2 and C9 carbonyl groups of the pigment molecules are undisturbed. Having shown the lack of sensitivity to pressure of the binding site interactions, which are known to modulate the absorption spectrum, we feel that it is relatively safe to attribute the pressure-induced red shift broadly to solvatochromic effects and, in particular, to the modulation of the pigment-pigment interactions by the pressure. This paper represents the first vibrational study of photosynthetic complexes at high pressure and the first application of FT Raman spectroscopy to biological molecules at high pressure.

Bacterial Proteins↗
PubMed1998

Highly efficient and versatile synthesis of libraries of constrained beta-strand mimetics.

The general approach of using a bicyclic template to produce inhibitors of the protease superfamily of enzymes has been investigated. The Diels Alder cycloaddition reaction on solid support has been found to be highly efficient for the synthesis of libraries of compounds that mimic the beta-strand secondary structure of proteins. Several potent and selective inhibitors of proteases have been discovered.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed1997

Influence of the protein binding site on the absorption properties of the monomeric bacteriochlorophyll in Rhodobacter sphaeroides LH2 complex.

Resonance Raman spectroscopy was performed on peripheral light-harvesting proteins from Rhodobacter sphaeroides in which the residue betaArg-10 has been modified by site-selected mutagenesis. We show that this residue is indeed involved (as proposed by X-ray crystallographic studies on the LH2 complex from Rhodopseudomonas acidophila), in an H-bond with the acetyl carbonyl of the 800 nm-absorbing BChl in these proteins (B800), and that the presence of such an H-bond induces a ca. 10 nm red shift of the lowest energy transition (Qy) of this molecule. Moreover, other parameters involved in the fine tuning of the absorption of the B800 molecules may be determined from our experiments, and we propose that the local electromagnetic properties of the B800 binding site may induce an additional 10 nm red shift of this transition. These results constitute the first experimental evidence for the parameters able to modify in vivo the absorption of "monomeric" BChl molecules, i.e. BChl not involved in strong excitonic interactions, and will be of great help for understanding the absorption properties of such pigments in other light-harvesting systems.

Bacteriochlorophylls↗
PubMed1981

Decreased sensitivity of human platelets to PGI2 during long-term intraarterial prostacyclin infusion in patients with peripheral vascular disease--a rebound phenomenon?

During successful treatment of peripheral vascular disease with synthetic prostacyclin no alteration in platelet function was reported (1). In 8 patients infused with synthetic prostacyclin continuously for 7 days intraarterially, the platelet function was monitored. Special attention was drawn to the platelet sensitivity in vitro for PGI2, which is discussed as an important factor maintaining the hemostatic balance. In all the patients with peripheral vascular disease between 24 and 48 hours after the beginning of the infusion a sudden decrease in platelet sensitivity accompanied by an increase in platelet count could be seen. These dramatic alterations representing probably a rebound phenomenon occurring during long-term PGI2-treatment might be an explanation for a non-beneficial effect of the treatment and in some cases a limiting factor for the continuation of the infusion itself. It is not clear, if this rebound phenomenon is due to a stimulation of an endogenous inhibitor, lowering the synthesis of a naturally occurring substance acting against this inhibitor or tachyphylaxia.

Aged↗
PubMedDate not supplied

Synthesis and reactivity of aryl nitrogen mustard-oligodeoxyribonucleotide conjugates.

A versatile method is described for preparing aryl nitrogen mustard-oligodeoxyribonucleotide (mustard-ODN) conjugates under anhydrous conditions. The chemistry uses DMSO soluble triethylammonium or tributylammonium salts of the ODNs. A G/A motif triplex forming ODN was chosen for study since it had been shown earlier to bind with high affinity and specificity to a duplex DNA target. A 5'-hexylamine derivative of this ODN was reacted with three different 2,3,5,6-tetrafluorophenyl ester derivatives of aryl nitrogen mustards which were designed to have different alkylation rates. An HPLC assay was used to determine reaction rates of these mustard-ODNs under various conditions. The reactivity of the mustard groups depended on chloride concentration and the presence of nucleophiles. Conjugation of mustards to G/A-containing ODNs decreased their aqueous stability. Hydrolysis and alkylation rates of these agents were consistent with reaction via an aziridinium intermediate. Rates of sequence specific alkylation within a triplex were determined by denaturing gel electrophoresis and shown to depend on inherent reactivity of the mustard group. The improved synthesis and chemical characterization of mustard-ODNs should facilitate their use as sequence specific alkylating agents and as probes for nucleic acid structure.

Alkylation↗