Substituting azobenzene for proline in melittin to create photomelittin: A light-controlled membrane active peptide.

In this article we present the synthesis and characterization of a new form of the membrane active peptide melittin: photomelittin. This peptide was created by substituting the proline residue in melittin for a synthetic azobenzene amino acid derivative. This azobenzene altered the membrane activity of the peptide while retaining much of the secondary structure. Furthermore, the peptide demonstrates added light-dependent activity in leakage assays. There is a 1.5-fold increase in activity when exposed to UV light as opposed to visible light. The peptides further exhibit light-dependent hemolytic activity against human red blood cells. This will enable future studies optimizing photomelittin and other azobenzene-containing membrane active peptides for uses in medicine, drug delivery, and other biotechnological applications.

UV and bacteriophages as a chemical-free approach for cleaning membranes from anaerobic bioreactors.

Anaerobic membrane bioreactor (AnMBR) for wastewater treatment has attracted much interest due to its efficacy in providing high-quality effluent with minimal energy costs. However, membrane biofouling represents the main bottleneck for AnMBR because it diminishes flux and necessitates frequent replacement of membranes. In this study, we assessed the feasibility of combining bacteriophages and UV-C irradiation to provide a chemical-free approach to remove biofoulants on the membrane. The combination of bacteriophage and UV-C resulted in better log cells removal and ca. 2× higher extracellular polymeric substance (EPS) concentration reduction in mature biofoulants compared to either UV-C or bacteriophage alone. The cleaning mechanism behind this combined approach is by 1) reducing the relative abundance of Acinetobacter spp. and selected bacteria (e.g., Paludibacter, Pseudomonas, Cloacibacterium, and gram-positive Firmicutes) associated with the membrane biofilm and 2) forming cavities in the biofilm to maintain water flux through the membrane. When the combined treatment was further compared with the common chemical cleaning procedure, a similar reduction on the cell numbers was observed (1.4 log). However, the combined treatment was less effective in removing EPS compared with chemical cleaning. These results suggest that the combination of UV-C and bacteriophage have an additive effect in biofouling reduction, representing a potential chemical-free method to remove reversible biofoulants on membrane fitted to an AnMBR.

Shot Noise Explains the Petkau 22Na+ Result for Rupture of a Model Phospholipid Membrane.

The action of free radicals is believed responsible for much or most biological injury resulting from exposure to ionizing radiation. These molecules in solution possess short lifetimes on the order of nanoseconds to microseconds. As a result, the dose-which measures the energy dissipated in tissue due to radiolysis-should not be considered a reliable indicator of the free radical concentration, nor of the chemical effects that follow from it. Rather, the chemical state of affected tissue is properly represented only by the dissipated power, which describes the distribution of energy with time. The present report demonstrates the validity of this assertion using data contained in a report describing a benchtop experiment published in 1972. The experiment used the visible rupture of a model phospholipid membrane as a means to quantify the degree of chemical insult caused by ionizing radiation. The experiment found that beta doses in the range from 1-10 rad were equivalent to x-ray rupture doses of 3,500 rad. This report demonstrates that the experimental results are convincingly explained by reference to the properly calculated time-averaged dissipated power due to beta decay. The theoretical explanation is derived by analogy to a well-understood result from electronic systems known as shot noise. If the result described in this report is demonstrated to extrapolate from the benchtop to living systems, then it is likely that exposure to beta radiation via internal incorporation is far more hazardous than commonly believed. The finding could be revolutionary in the field of health physics.

Synergistic inactivation and mechanism of thermal and ultrasound treatments against Bacillus subtilis spores.

Some Bacillus species are causative agents of food spoilage and a wide array of diseases. Due to their ability to form highly heat-resistant spores, it is of great interest to develop more effective inactivation strategies whereby these spores could be inactivated. Therefore, this work assessed inactivation of thermal and ultrasound treatments against Bacillus subtilis spores. The study further investigated the thermosonication (thermal and ultrasound, TS) -induced inactivation to the spores through a combination of morphology observation and internal factor analyses. The results of TS indicated that the TS combination synergistically inactivated spores by the maximum log reduction of 2.43 ±â€¯0.08 at 80 °C and 20 W/ml and caused severe cell damage. The visual images revealed that the destructive mode of action of TS had multitarget sites, including coat, cortex, and inner membrane. Three distinct sub-populations were detected by Flow cytometry (FCM), and an unknown step with some physical compromise of the spore's inner membrane and partially hydrolyzed cortex involving the three steps model of inactivation was suggested. The combination of DPA (pyridine-2,6 dicarboxylic acid) content and the relative viabilities of the fractions suggested that during the TS treatment DPA release took place largely after spore death. The dead spores that retained DPA germinated relatively normally, but outgrow poorly, indicating that some key enzymes of intermediary metabolism has been damaged by TS treatment. Such understanding of the lethal action of TS may lead to the development of novel strategies involving spore destruction.

Adaptations in rod outer segment disc membranes in response to environmental lighting conditions.

The light-sensing rod photoreceptor cell exhibits several adaptations in response to the lighting environment. While adaptations to short-term changes in lighting conditions have been examined in depth, adaptations to long-term changes in lighting conditions are less understood. Atomic force microscopy was used to characterize the structure of rod outer segment disc membranes, the site of photon absorption by the pigment rhodopsin, to better understand how photoreceptor cells respond to long-term lighting changes. Structural properties of the disc membrane changed in response to housing mice in constant dark or light conditions and these adaptive changes required output from the phototransduction cascade initiated by rhodopsin. Among these were changes in the packing density of rhodopsin in the membrane, which was independent of rhodopsin synthesis and specifically affected scotopic visual function as assessed by electroretinography. Studies here support the concept of photostasis, which maintains optimal photoreceptor cell function with implications in retinal degenerations.

Reversible control of current across lipid membranes by local heating.

Lipid membranes are almost impermeable for charged molecules and ions that can pass the membrane barrier only with the help of specialized transport proteins. Here, we report how temperature manipulation at the nanoscale can be employed to reversibly control the electrical resistance and the amount of current that flows through a bilayer membrane with pA resolution. For this experiment, heating is achieved by irradiating gold nanoparticles that are attached to the bilayer membrane with laser light at their plasmon resonance frequency. We found that controlling the temperature on the nanoscale renders it possible to reproducibly regulate the current across a phospholipid membrane and the membrane of living cells in absence of any ion channels.

Pulsed electric field processing preserves the antiproliferative activity of the milk fat globule membrane on colon carcinoma cells.

The present work evaluated the effect of processing on the antiproliferative activities of milk fat globule membrane (MFGM) extracts. The antiproliferative activity on human adenocarcinoma HT-29 cells of untreated MFGM extracts were compared with those extracted from pasteurized cream, thermally treated cream, or cream subjected to pulsed electrical field (PEF) processing. The PEF with a 37 kV/cm field strength applied for 1,705µs at 50 and 65°C was applied to untreated cream collected from a local dairy. Heating at 50 or 65°C for 3min (the passage time in the PEF chamber) was also tested to evaluate the heating effect during PEF treatments. The MFGM extracted from pasteurized cream did not show an antiproliferative activity. On the other hand, isolates from PEF-treated cream showed activity similar to that of untreated samples. It was also shown that PEF induced interactions between ß-lactoglobulin and MFGM proteins at 65°C, whereas the phospholipid composition remained unaltered. This work demonstrates the potential of PEF not only a means to produce a microbiologically safe product, but also as a process preserving the biofunctionality of the MFGM.

[Radiobiology of ablative dose in stereotactic irradiation: data update]. / Radiobiologie des doses ablatives en radiothérapie stéréotaxique: mise au point des données récentes.

Stereotactic radiotherapy is a radiation technique, which is becoming more and more available and applicable for physicians. A good efficacy and safety are observed in clinical practice. However, the radiobiology of ablative radiation is still under question. The radiobiological principles of the 5R have to be discussed. The roles of hypoxia and vascularization, more specifically, angiogenesis and vasculogenesis seem to be dominating.

Electron beam induced radiation damage in the catalyst layer of a proton exchange membrane fuel cell.

Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field-scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3-1 times λ), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided.

Membrane signaling induced by high doses of ionizing radiation in the endothelial compartment. Relevance in radiation toxicity.

Tumor areas can now be very precisely delimited thanks to technical progress in imaging and ballistics. This has also led to the development of novel radiotherapy protocols, delivering higher doses of ionizing radiation directly to cancer cells. Despite this, radiation toxicity in healthy tissue remains a major issue, particularly with dose-escalation in these new protocols. Acute and late tissue damage following irradiation have both been linked to the endothelium irrigating normal tissues. The molecular mechanisms involved in the endothelial response to high doses of radiation are associated with signaling from the plasma membrane, mainly via the acid sphingomyelinase/ceramide pathway. This review describes this signaling pathway and discusses the relevance of targeting endothelial signaling to protect healthy tissues from the deleterious effects of high doses of radiation.

Photoelectron dynamics in x-ray free-electron-laser diffractive imaging of biological samples.

X-ray free electron lasers hold the promise of enabling atomic-resolution diffractive imaging of single biological molecules. We develop a hybrid continuum-particle model to describe the x-ray induced damage and find that the photoelectron dynamics and electrostatic confinement strongly affect the time scale of the damage processes. These phenomena are not fully captured in hydrodynamic modeling approaches.

Effects of photooxidation on membrane integrity in Salix nigra seeds.

BACKGROUND AND AIMS: Salix nigra seeds are desiccation-tolerant, as are orthodox seeds, although in contrast to other orthodox seeds they lose viability in a few weeks at room temperature. They also differ in that the chloroplasts of the embryo tissues conserve their chlorophyll and endomembranes. The aim of this paper was to investigate the role of chlorophyll in seed deterioration. METHODS: Seeds were aged at different light intensities and atmospheric conditions. Mean germination time and normal and total germination were evaluated. The formation of free radicals was assessed using electronic spin resonance spectroscopy, and changes in the fatty acid composition from phospholipids, galactolipids and triglycerides using gas-liquid chromatography. Membrane integrity was studied with electronic spin resonance spin probe techniques, electrolyte leakage and transmission electron microscopy. KEY RESULTS: Light and oxygen played an important role in free-radical generation, causing a decrease in normal germination and an increase in mean germination time. Both indices were associated with a decrease in polyunsaturated fatty acids derived from membrane lipids as phospholipids and galactolipids. The detection of damage in thylakoid membranes and an increase in plasmalemma permeability were consistent with the decrease in both types of lipids. Triglycerides remained unchanged. Light-induced damage began in outermost tissues and spread inwards, decreasing normal germination. CONCLUSIONS: Salix nigra seeds were very susceptible to photooxidation. The thylakoid membranes appeared to be the first target of the photooxidative process since there were large decreases in galactolipids and both these lipids and the activated chlorophyll are contiguous in the structure of that membrane. Changes in normal germination and mean germination time could be explained by the deteriorative effects of oxidation.

Membrane perturbation by an external electric field: a mechanism to permit molecular uptake.

Electropermeabilisation is a well established physical method, based on the application of electric pulses, which induces the transient permeabilisation of the cell membrane. External molecules, otherwise nonpermeant, can enter the cell. Electropermeabilisation is now in use for the delivery of a large variety of molecules, as drugs and nucleic acids. Therefore, the method has great potential in the fields of cancer treatment and gene therapy. However many open questions about the underlying physical mechanisms involved remain to be answered or fully elucidated. In particular, the induced changes by the effects of the applied field on the membrane structure are still far from being fully understood. The present review focuses on questions related to the current theories, i.e. the basic physical processes responsible for the electropermeabilisation of lipid membranes. It also addresses recent findings using molecular dynamics simulations as well as experimental studies of the effect of the field on membrane components.

Biophysical effects of electric fields on membrane water interfaces: a mini review.

Lipid-water interfaces are dielectric transition regions. Their local organizations are highly sophisticated. They are sensitive to electric field with dramatic consequences on the global membrane organization and function. The importance of using local values of parameters (e.g. dielectric constant) near water-solution interface due to hydration and different electrostatic effects is often neglected in the description of cellular functions. Structural changes in the lipid layer are induced by minute changes in the electric properties of the interface. They bring alterations in the structure and oligomerization of membrane proteins.

Protection of DNA and membrane from gamma radiation induced damage by gallic acid.

Gallic acid (3,4,5-trihydroxybenzoic acid, GA) is a naturally occurring plant phenol. In vitro and in vivo studies have shown that this phytochemical protected DNA and membranes against ionizing radiation. Rat liver microsomes and plasmid pBR322 DNA were exposed to various doses of gamma radiation in presence and absence of GA. Exposure of the microsomes to gamma radiation resulted in the formation of peroxides of membrane lipids measured as thiobarbituric acid reactive substances and presence of GA during irradiation prevented the formation of lipid peroxidation. Gamma irradiation of plasmid DNA resulted in induction of strand breaks in DNA resulting in disappearance of the supercoiled (ccc) form. Presence of GA during irradiation protected the DNA from undergoing the strand breaks. In in vivo studies it was found that whole body exposure of mice to gamma radiation (4 Gy) increased the formation of lipid peroxides in various tissues and damage to cellular DNA (as measured by alkaline comet assay) in peripheral blood leucocytes. Administration of GA to mice prior to whole body radiation exposure reduced the peroxidation of lipids and the damage to the cellular DNA indicating in vivo radiation protection of membranes and DNA by GA.

[Investigation of the effects of drugs and UV radiation on biological and artificial membranes]. / Gyógyszermolekulák es UV-fény hatásának vizsgálata biológiai- es modellmembránokon.

Investigation of the effects exerted by different physical and chemical agents on biological and model-membranes is of prominent importance. Recently, a general trend can be observed in the formulation of drugs: incorporation of the drugs into liposomes. Knowledge of the molecular interactions between the transporting lipids and the incorporated agents is therefore very important. Nowadays, the increased environmental UV radiation requires investigation of the effects of the UV radiation exerted on biological membranes. Beside of modeling biological effects, studies on the effects of the UV radiation on model membranes can result in new knowledge on the stability of the liposomes containing phototoxic drugs. During my study, three different methods (EPR spectroscopy, DSC and light scattering measurements) have been applied to investigate the molecular interactions between drugs and the lipid molecules. Derivatives of the morphine as well as the (fluoro)quinolones mainly interact with the headgroups of the lipid molecules resulting in an increase of the molecular ordering of the lipids. My observation that drugs with protonable/deprotonable groups can modify the membrane-fluidity due to specific, local interactions with the lipid/stearic acid molecules of a membrane depending on the pH as well, call attention to choose optimal pH-interval for such drug formulations. Investigating the UVA effect on human fibroblast cell line I concluded that a decrease in the membrane fluidity due to UVA radiation can be detected only at doses higher, than 150 kJ/m2, and close to the lipid head groups.

[Radioenzymatic investigation of membrane and soluble forms of angiotensin-converting enzyme in acetate-phosphate buffer]. / Radioénzimologicheskoe izuchenie membrannoi i rastvorimoi form angiotenzinprevrashchaiushchego fermenta v atsetatno-fosfatnom bufere.

The dose response of soluble and membrane forms of angiotensin-converting enzyme to gamma-irradiation is investigated at different pH values of the medium and at different concentrations of acetate-phosphate buffer. Membrane form of the enzyme is more stable shows principally other conformational equilibrium than the soluble form. "Splitted" activation peaks on the curves of the enzyme dose response are observed.

Role of lycopene in recovery of radiation induced injury to mammalian cellular organelles.

Whole body exposure of male rats to 7 Gy gamma irradiation increased lipid peroxidation in the liver resulting in biomembrane damage of subcellular structures and release of their enzymes. This is evidenced by increase of thiobarbituric acid-reactive substances (TBARS) in mitochondria, lysosomes and microsomes. This was associated with a decrease in activity of the enzymes specific for each subcellular fraction; namely, mitochondrial glutamate dehydrogenase (GDH), lysosomal beta-glucuronidase and microsomal glucose 6-phosphatase. This was paralleled by an increased activity of these enzymes in the cytosol. Rats were supplemented with lycopene, a carotenoid present in tomatoes (5 mg/kg weight/day), by gavage, for 7 days before exposure to 7 Gy gamma irradiation. This resulted in diminishing amount of TBARS recorded for each subcellular structure in the liver of irradiated animals. Significant amelioration in the decrease recorded for the activity of mitochondrial glutamate dehydrogenase, lysosomal beta-glucuronidase and microsomal glucose 6-phosphatase was observed. This was associated with significant amelioration in the increase recorded for the activity of these enzymes in the cytosol. It is postulated that lycopene could play an important role in the recovery of the integrity of biological membranes of the liver after radiation injury.

Thermophotovoltaic (TPV) properties of hornet cuticle as dependent on relative humidity.

This paper deals with the thermophotovoltaic (TPV) properties of the cuticle of the Oriental hornet as assessed over time under different regimens of relative humidity (RH). The tests were run at two levels of RH, namely, 30% vs. 90%. Each experiment entailed measuring the cuticular voltage and current in the dark as compared to under illumination (white light = 700 Lux), and at a temperature range of 20-30 degrees C. It was found that increase in the RH level boosts the current values by 2-3 orders of magnitude; contrariwise, the voltage values rise by about three times with drop in the RH. At high RH, the changes in current become rhythmical and each cycle of warming-cooling assumes a distinctly cyclic pattern. Under illumination, the current decreases, the polarity reverses and the resistance increases. The obtained results are describable by a model of electric conductance upon a surface, in this case the hornet cuticle; the findings are also discussed and compared with similar phenomena recorded from other substances possessing the properties of organic semiconductors.