1,721,360 research outputs found
The proton sensitivity of Fluorescent Proteins: towards intracellular pH indicators
No full textOn account of the presence of an ionizable phenol group on their chromophore, most fluorescent proteins display pH-sensitive absorption and fluo- rescence emission bands. This property has great implications for most applications that involve FPs as intracellular markers of target proteins. The photophysical modulation of pH sensitivity relies upon a complex network of exchange reaction pathways involving the chromophore and funneling protons in and out the protein structure. In parallel with the fast-growing use of FPs as intracellular probes, many groups reported on the use of FP variants as genetically-encodable pH indicators of intracellular compartments that cannot be probed using conventional pH-sensitive dyes. These pH indicators shed light on many cell functions strongly coupled with local pH. Here, we shall review both the properties that make FPs so efficient as intracellular pH indicators and the probes that are more utilized by the scientific community
Dolichol: A Natural Biomarker of Aging Endowed With a Photoenhanced Highly-Effective Solar Filter Activity
No full textDolichol is a polysoprenoid lipid ubiquitous in eukaryotic cell membranes. Its molecular structure comprises a sequence of E and Z unsatured isoprene units tethered by a satured isoprene unit bearing a hydroxyl group. Dolichol is mostly present in the native form or esterified by lipid acids, and it is thought to locate in the innermost part of the membrane double layer, intertwining with the hydrophobic terminus of the phospholipids. In spite of this peculiar arrangement, no clear biological function of dolichol has been evidenced yet, although a minor dolichyl phosphate pool is known to assist the N-glycosylation of proteins in the endoplasmic reticulum. Dolichol was recently found to strongly interact with free-radicals, leading to a fast molecular disruption without peroxidized by-products. This scavenging property may explain why dolichol accumulates with age, representing an excellent biomarker of the ageing process also sensitive to ageing-preventing dietary regimes in living animals. Furthermore, dolichol was shown to possess photoprotective characteristics towards UV radiation. On account of its high biocompatibility, its free-radical scavenging and photoprotective properties, and its easy preparation from vegetable extracts, dolichol has been proposed as main components for dermatological and cosmetic compositions. The scientific background and the related patents are reviewed here
Intracellular pH measurements made simple by fluorescent protein probes and the phasor approach to fluorescence lifetime imaging
No full textA versatile pH-dependent fluorescent protein was applied to intracellular pH measurements by means of the phasor approach to fluorescence lifetime imaging. By this fit-less method we obtain intracellular pH maps under resting or altered physiological conditions by single-photon confocal or two-photon microscopy. RI Bizzarri, Ranieri/H-1779-201
Fluorescent Recovery after Photobleaching (FRAP) Analysis of Nuclear Export Rates Identifies Intrinsic Features of Nucleocytoplasmic Transport
No full textA quantitative description of carrier-mediated nuclear export in live cells is presented. To this end, we fused a prototypical leucine-rich nuclear export signal (NES) to GFP as a cargo model and expressed the fluorescent chimera in live CHO-K1 cells. By modeling FRAP data, we calculate the NES affinity for the export machinery and the maximum rate of nuclear export achievable at saturation of endogenous carriers. The measured active-export time through the Nuclear Pore Complex (NPC) is 18 ms, remarkably similar to the previously determined active-import rate. Also, our results reveal that active export/import and active export/passive diffusion fluxes are uncoupled, thus complementing previous reports on active import/passive diffusion uncoupling. These findings suggest differential gating at the NPC level
Quantitative optical lock-in detection for quantitative imaging of switchable and non-switchable components
No full textReversible photoswitching has been proposed as a way to identify molecules that are present in small numbers over a large, non-switching, background. This approach, called optical-lock-indetection (OLID) requires the deterministic control of the fluorescence of a photochromic emitter through optical modulation between a bright (on) and a dark state (off). OLID yields a high-contrast map where the switching molecules are pinpointed, but the fractional intensities of the emitters are not returned. The present work presents a modified OLID approach (quantitative OLID or qOLID) that yields quantitative information of the switching (f(SW)) and non-switching (f(NS)) components. After the validation of the method with a sample dataset and image sequence, we apply qOLID to measurements in cells that transiently express the photochromic protein EYQ1. We show that qOLID is efficient in separating the modulated from the non-modulated signal, the latter deriving from background/autofluorescence or fluorophores emitting in the same spectral region. Finally, we apply qOLID to Forster (Fluorescence) Resonance Energy Transfer (FRET) imaging. We here demonstrate that qOLID is able to highlight the distribution of FRET intensity in a sample by using a photochromic donor and a non-photochromic acceptor
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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