Thermal degradation kinetics of the phycocyanin from Spirulina platensis

The cyanobacterium Spirulina platensis is a source of pigments, such as phycocyanin, which is used in the food, cosmetic and pharmaceutical industries. The thermal degradation kinetics of the liquid extract at pH values of 5, 6 and 7 was studied, evaluating its stability between 50 and 65 °C. The kinetic model was assumed and validated as being of the first order. Between 50 and 55 °C the extract was more stable at pH 6 and between 57 and 65 °C at pH 5, but was shown to be increasingly unstable at pH 7 as the temperature of the treatment increased. The addition of sorbitol between 10 and 50% (w/w) in the treatment at 62 °C for 30 min increased the half-life values of the phycocyanin extract, proving that its de-colorization was related to degradation of the protein chain.     

G protein-coupled receptor kinase 2 (GRK2) in migration and inflammation

G protein-coupled receptor kinase 2 (GRK2) is a key modulator of G protein-coupled receptors and other plasma membrane receptors stimulated by chemotactic messengers. On top of that, GRK2 has been reported to interact with a variety of signal transduction proteins related to cell migration such as MEK, Akt, PI3Kgamma or GIT. Interestingly, the levels of expression and activity of this kinase are altered in a number of inflammatory disorders (as rheumatoid arthritis or multiple sclerosis), thus suggesting that it may play an important role in the onset or development of these pathologies. This review summarizes the mechanisms involved in the control of GRK2 expression and function and highlights novel functional interactions of this protein that might help to explain how altered GRK2 levels affects cell migration in different cell types and pathological settings.     

Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient

Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L⁻¹) to northern Spain (0.35 mg L⁻¹), but with a sharp increase in southern Spain (0.9 mg L⁻¹). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 μg L⁻¹) to València (150 μg L⁻¹). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.     

Portal protein diversity and phage ecology

Oceanic phages are critical components of the global ecosystem, where they play a role in microbial mortality and evolution. Our understanding of phage diversity is greatly limited by the lack of useful genetic diversity measures. Previous studies, focusing on myophages that infect the marine cyanobacterium Synechococcus, have used the coliphage T4 portal-protein-encoding homologue, gene 20 (g20), as a diversity marker. These studies revealed 10 sequence clusters, 9 oceanic and 1 freshwater, where only 3 contained cultured representatives. We sequenced g20 from 38 marine myophages isolated using a diversity of Synechococcus and Prochlorococcus hosts to see if any would fall into the clusters that lacked cultured representatives. On the contrary, all fell into the three clusters that already contained sequences from cultured phages. Further, there was no obvious relationship between host of isolation, or host range, and g20 sequence similarity. We next expanded our analyses to all available g20 sequences (769 sequences), which include PCR amplicons from wild uncultured phages, non-PCR amplified sequences identified in the Global Ocean Survey (GOS) metagenomic database, as well as sequences from cultured phages, to evaluate the relationship between g20 sequence clusters and habitat features from which the phage sequences were isolated. Even in this meta-data set, very few sequences fell into the sequence clusters without cultured representatives, suggesting that the latter are very rare, or sequencing artefacts. In contrast, sequences most similar to the culture-containing clusters, the freshwater cluster and two novel clusters, were more highly represented, with one particular culture-containing cluster representing the dominant g20 genotype in the unamplified GOS sequence data. Finally, while some g20 sequences were non-randomly distributed with respect to habitat, there were always numerous exceptions to general patterns, indicating that phage portal proteins are not good predictors of a phage's host or the habitat in which a particular phage may thrive.     

Attention and awareness in stage magic: turning tricks into research

Just as vision scientists study visual art and illusions to elucidate the workings of the visual system, so too can cognitive scientists study cognitive illusions to elucidate the underpinnings of cognition. Magic shows are a manifestation of accomplished magic performers' deep intuition for and understanding of human attention and awareness. By studying magicians and their techniques, neuroscientists can learn powerful methods to manipulate attention and awareness in the laboratory. Such methods could be exploited to directly study the behavioural and neural basis of consciousness itself, for instance through the use of brain imaging and other neural recording techniques.     

An analysis of the positional distribution of DNA motifs in promoter regions and its biological relevance

Background  

Motif finding algorithms have developed in their ability to use computationally efficient methods to detect patterns in biological sequences. However the posterior classification of the output still suffers from some limitations, which makes it difficult to assess the biological significance of the motifs found. Previous work has highlighted the existence of positional bias of motifs in the DNA sequences, which might indicate not only that the pattern is important, but also provide hints of the positions where these patterns occur preferentially.     

The calcium channel β2 (CACNB2) subunit repertoire in teleosts

Background  

Cardiomyocyte contraction is initiated by influx of extracellular calcium through voltage-gated calcium channels. These oligomeric channels utilize auxiliary β subunits to chaperone the pore-forming α subunit to the plasma membrane, and to modulate channel electrophysiology [1]. Several β subunit family members are detected by RT-PCR in the embryonic heart. Null mutations in mouse β2, but not in the other three β family members, are embryonic lethal at E10.5 due to defects in cardiac contractility [2]. However, a drawback of the mouse model is that embryonic heart rhythm is difficult to study in live embryos due to their intra-uterine development. Moreover, phenotypes may be obscured by secondary effects of hypoxia. As a first step towards developing a model for contributions of β subunits to the onset of embryonic heart rhythm, we characterized the structure and expression of β2 subunits in zebrafish and other teleosts.     

Connexin 30.3 is expressed in the kidney but not regulated by dietary salt or high blood pressure

Several isoforms of connexin (Cx) proteins have been identified in a variety of tissues where they play a role in intercellular communication, either as the components of gap junctions or as large, nonselective pores known as hemichannels. This investigation seeks to identify the localization and regulation of Cx30.3 in mouse, rat, and rabbit kidney using a Cx30.3(+/lacZ) transgenic approach and immunofluorescence. Cx30.3 was detected in all three species and predominantly in the renal medulla. Both the nuclear lacZ staining indicative of Cx30.3 expression and indirect immunohistochemistry provided the same results. Cx30.3 immunolabeling was mainly punctate in the mouse, typical for gap junctions. In contrast, it showed continuous apical plasma membrane localization in certain tubule segments in the rat and rabbit kidney, suggesting that it may also function as hemichannels. In the cortex, Cx30.3 was localized in the intercalated cells of the cortical collecting duct, because the immunoreactive cells did not label for AQP2, a marker for principal cells. In the medulla, dense Cx30.3 staining was confined to the ascending thin limbs of the loop of Henle, because the immunoreactive cells did not label for AQP1, a marker of the descending thin limbs. Immunoblotting studies indicated that Cx30.3 expression was unchanged in response to either high or low salt intake or in spontaneously hypertensive rats. Cx30.3 appears to be constitutively expressed in certain renal tubular segments and cells and its role in overall kidney function remains to be investigated.     

Photophysical characterization and flow cytometry applications of cholylamidofluorescein, a fluorescent bile acid scaffold

Cholylamidofluorescein (CamF) has been selected as a fluorescent bile acid scaffold to perform a full characterization of its photophysical properties. In aqueous medium, under nitrogen, the absorption spectrum of CamF was expectedly dependent on pH. Under air, the presence of CO(2) resulted in a partial protonation of the photoactive form, reducing the absorbance of CamF. The fluorescence spectrum of CamF in ethanol (lambda(exc) = 481 nm) showed a broad band with maximum at 518 nm; the fluorescence quantum yield was 0.67, and the fluorescence lifetime was 4.8 ns. Laser flash photolysis of CamF showed the triplet state transient with a broad maximum at ca. 540 nm and a lifetime of 19 mus. Flow cytometric kinetic assay of CamF uptake in real time was performed in suspensions of rat hepatocytes, showing that living hepatocytes accumulated slowly but constantly CamF along the 5-minute experimental period. Besides, intracellular fluorescence of live cells was found to be clearly dependent on the extracellular concentration of CamF. Thus, flow cytometry has allowed us to demonstrate that CamF is specifically taken up by living rat hepatocytes in a concentration-dependent fashion, suggesting the suitability of this molecule for further studies on bile-acid transport in liver cells.