Erythrocyte spectrin maintains its segmental motions on oxidation: a spin-label EPR study.

The segmental motions of cross-linked erythrocyte skeletal protein (spectrin-actin-protein 4.1) samples, labeled with nitroxide spin labels, were monitored by conventional first-harmonic and saturation transfer second-harmonic electron paramagnetic resonance methods. Skeletal proteins were extracted from human red blood cells and treated with three oxidative reagents (diamide, hydrogen peroxide, and phenylhydrazine) to cross-link sulfhydryl groups and with one fixative reagent (glutaraldehyde) to cross-link lysine residues. The treatments provided extensive cross-linking between spectrin-actin-protein 4.1 molecules, as determined by gel electrophoresis, and surface charge modification, as determined by pl measurements. However, segmental motions of the cross-linked skeletal proteins remained generally similar to those in normal skeletal proteins. Both the weakly immobilized and the strongly immobilized motions were similar in cross-linked and control samples. Small differences in some motional components were detected. In some cases, faster mobilities were observed, with approximately 5% of the strongly immobilized motions converted to the weakly immobilized motions in the cross-linked samples. It is often believed that the consequence of membrane protein oxidation is restricted protein dynamics, giving membrane rigidity. However, our studies provide needed experimental evidence to indicate that segmental motions are maintained with very little modification even in the presence of extensive cross-linking. Thus cross-linking does not restrict the internal molecular flexibility that gives rise to segmental motions.     

Sources and sinks in population biology

The various habitats inhabited by a given species are never of the same quality. When demographic models take into account this habitat heterogeneity, the source-sink concept naturally emerges: a local demographic surplus arises in good quality habitats (source), and a local demographic deficit occurs in habitats of poor quality (sink). Within a landscape, a permanent migration of propagules or individuals from source to sink habitats may lead to a stabilization of the overall demographic system. This simple situation, explored in the recent literature, has surprising properties. In particular, it requires a change in our view of classical concepts such as ecological niche and carrying capacity, it can explain the existence and persistence of local maladaptation and it can improve conservation practice.     

The use of confocal microscopy in the investigation of cell structure and function in the heart,vascular endothelium and smooth muscle cells

In recent years, fluorescence microscopy imaging has become an important tool for studying cell structure and function. This non invasive technique permits characterization, localisation and qualitative quantification of free ions, messengers, pH, voltage and a pleiad of other molecules constituting living cells. In this paper, we present results using various commercially available fluorescent probes as well as some developed in our laboratory and discuss the advantages and limitations of these probes in confocal microscopy studies of the cardiovascular system.     

Effects of water deficit on the activity of nitrate reductase and content of sugars, nitrate and free amino acids in the leaves and roots of sunflower and white lupin plants growing under two nutrient supply regimes

The effects of soil drying on the activity of nitrate reductase (NR; EC 1.6.6.6) were studied in Helianthus annuus L. and non-nodulated Lupinus albus L. plants growing under two nutrient supply regimes. NR activity was assessed in leaf and root extracts by measuring the activity of the unphosphorylated active form (NR_act), the maximal extractable activity (NR_max) and the activation state. To obtain an insight into potential signalling compounds, nitrate, free amino acids and soluble sugars were also quantified. In both species, foliar NR_act and NR_max were negatively affected by soil drying and a decreased supply of nutrients, the observed changes in NR activity being linearly correlated with the depletion of nitrate. Similar results were obtained in the roots of sunflower. Conversely, in white lupin roots, NR_max was found to be independent of tissue nitrate concentration. Regardless of the species and organ, the activation state of the enzyme was unaffected by the nutrient supply regime. In well-watered sunflower roots, only about 50% of the existing NR was unphosphorylated, but the activation state increased significantly in response to drought. In contrast, lupin roots always exhibited NR activation state values close to 80%, or even higher. At the leaf level, the NR activation state was hardly changed in response to soil drying. The observed changes in the concentrations of soluble sugars and free amino acids are discussed in terms of their possible contribution to the variations in NR activity.     

6-h advances alter circadian activity patterns,fasting glucose,and insulin levels in C57BL6/J mice

Chronobiological disruptions, including shift work, have been linked to a number of disorders such as fatigue and diabetes. Additionally, there is evidence to support that exercise cannot only counteract fatigue and the onset of diabetes, but also alleviate the other negative symptoms associated with shift work. Therefore, the present study investigated the effects of wheel running and monthly 6-h phase advances on the circadian locomotor activity patterns and glucose and insulin levels in C57BL6/J mice. 6-h phase advances produced decreases in fasting glucose and increases in insulin, and wheel-running was able to alleviate the spike in insulin secretion. Additionally, mice experiencing the shift increased their food intake, despite having no change in body mass. Circadian wheel-running activity was also altered in phase-advanced mice. These results provide further evidence that chronobiological disruptions can lead to alterations in physiology and behavior, and that exercise can alleviate some of those symptoms.     

Metal and metalloid containing natural products and a brief overview of their applications in biology,biotechnology and biomedicine

Bioinorganic natural product chemistry is a relatively unexplored but rapidly developing field with enormous potential for applications in biology, biotechnology (especially in regards to nanomaterial development, synthesis and environmental cleanup) and biomedicine. In this review the occurrence of metals and metalloids in natural products and their synthetic derivatives are reviewed. A broad overview of the area is provided followed by a discussion on the more common metals and metalloids found in natural sources, and an overview of the requirements for future research. Special attention is given to metal hyperaccumulating plants and their use in chemical synthesis and bioremediation, as well as the potential uses of metals and metalloids as therapeutic agents. The potential future applications and development in the field are also discussed.     

PRNP/prion protein regulates the secretion of exosomes modulating CAV1/caveolin-1-suppressed autophagy

Prion protein modulates many cellular functions including the secretion of trophic factors by astrocytes. Some of these factors are found in exosomes, which are formed within multivesicular bodies (MVBs) and secreted into the extracellular space to modulate cell-cell communication. The mechanisms underlying exosome biogenesis were not completely deciphered. Here, we demonstrate that primary cultures of astrocytes and fibroblasts from prnp-null mice secreted lower levels of exosomes than wild-type cells. Furthermore, prnp-null astrocytes exhibited reduced MVB formation and increased autophagosome formation. The reconstitution of PRNP expression at the cell membrane restored exosome secretion in PRNP-deficient astrocytes, whereas macroautophagy/autophagy inhibition via BECN1 depletion reestablished exosome release in these cells. Moreover, the PRNP octapeptide repeat domain was necessary to promote exosome secretion and to impair the formation of the CAV1-dependent ATG12–ATG5 cytoplasmic complex that drives autophagosome formation. Accordingly, higher levels of CAV1 were found in lipid raft domains instead of in the cytoplasm in prnp-null cells. Collectively, these findings demonstrate that PRNP supports CAV1-suppressed autophagy to protect MVBs from sequestration into phagophores, thus facilitating exosome secretion.