Variations In Membrane Structure Research Articles

Carbon Nanotube Uptake in Photosynthetic Bacteria for Near-infrared Imaging and Enhancing Bioelectricity Generation in Living Photovoltaics

The internalization of fluorescent single-walled carbon nanotubes (SWCNTs) in photosynthetic microbes can be exploited for applications ranging from energy conversion and imaging to biomolecule delivery. The internalization of these nanoparticles are largely controlled by the permeability of the surrounding microbial cell walls, which vary in surface charge density, composition, thickness, and elasticity across different species of microbes. Since these properties play a critical role in controlling internalization, the extension of SWCNT-based technologies to prokaryotes thus requires a comparative assessment of uptake across different species.Herein, we extend a technology previously developed for internalizing SWCNTs in prokaryotes, specifically unicellular Synechocystis sp. PCC 6803, to Nostoc punctiforme, a filamentous cyanobacterial strain known to differentiate into heterocysts under nitrogen starvation. Heterocysts are specialized compartments within the filament that are capable of nitrogen fixation. These compartments possess cell walls that are distinct from vegetative cells, conferring heterocysts with relatively reduced permeability and increased resistance to mechanical and osmotic stress. Using a combination of near-infrared (NIR) fluorescence, scanning electron microscopy (SEM), and Raman spectroscopy, we investigate the effects of different cell-wall architectures and SWCNT functionalizations on internalization. We specifically examine the effects of these distinct SWCNT-cell interactions on long-term cell integrity, activity, and viability. We further show that local variations in membrane structure can dictate the extent of SWCNT association and uptake in Nostoc cells. This dependency of nanoparticle internalization on cell type can be exploited for the development of novel cell-specific staining and imaging technologies.

Enhancing Pervaporation Membrane Selectivity by Incorporating Star Macromolecules Modified with Ionic Liquid for Intensification of Lactic Acid Dehydration.

Modification of polymer matrix by hybrid fillers is a promising way to produce membranes with excellent separation efficiency due to variations in membrane structure. High-performance membranes for the pervaporation dehydration were produced by modifying poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to facilitate lactic acid purification. Ionic liquid (IL), heteroarm star macromolecules (HSM), and their combination (IL:HSM) were employed as additives to the polymer matrix. The composition and structure of hybrid membranes were characterized by X-ray diffraction and FTIR spectroscopy. Scanning electron microscopy was used to investigate the membranes surface and cross-section morphology. It was established that the inclusion of modifiers in the polymer matrix leads to the change of membrane structure. The influence of IL:HSM was also studied via sorption experiments and pervaporation of water‒lactic acid mixtures. Lactic acid is an essential compound in many industries, including food, pharmaceutical, chemical, while the recovering and purifying account for approximately 50% of its production cost. It was found that the membranes selectively remove water from the feed. Quantum mechanical calculations determine the favorable interactions between various membrane components and the liquid mixture. With IL:HSM addition, the separation factor and performance in lactic acid dehydration were improved compared with pure polymer membrane. The best performance was found for (HSM: IL)-PPO/UPM composite membrane, where the permeate flux and the separation factor of about 0.06 kg m−2 h−1 and 749, respectively, were obtained. The research results demonstrated that ionic liquids in combination with star macromolecules for membrane modification could be a promising approach for membrane design.

Different Trafficking Phenotypes of Niemann-Pick C1 Gene Mutations Correlate with Various Alterations in Lipid Storage, Membrane Composition and Miglustat Amenability.

Niemann-Pick Type C (NPC) is an autosomal recessive lysosomal storage disease leading to progressive neurodegeneration. Mutations in the NPC1 gene, which accounts for 95% of the cases, lead to a defect in intra-lysosomal trafficking of cholesterol and an accumulation of storage material including cholesterol and sphingolipids in the endo-lysosomal system. Symptoms are progressive neurological and visceral deterioration, with variable onset and severity of the disease. This study investigates the influence of two different NPC1 mutations on the biochemical phenotype in fibroblasts isolated from NPC patients in comparison to healthy, wild type (WT) cells. Skin derived fibroblasts were cultured from one patient compound-heterozygous for D874V/D948Y mutations, which presented wild-type like intracellular trafficking of NPC1, and a second patient compound- heterozygous for I1061T/P887L mutations, which exhibited a more severe biochemical phenotype as revealed in the delayed trafficking of NPC1. Biochemical analysis using HPLC and TLC indicated that lipid accumulations were mutation-dependent and correlated with the trafficking pattern of NPC1: higher levels of cholesterol and glycolipids were associated with the mutations that exhibited delayed intracellular trafficking, as compared to their WT-like trafficked or wild type (WT) counterparts. Furthermore, variations in membrane structure was confirmed in these cell lines based on alteration in lipid rafts composition as revealed by the shift in flotillin-2 (FLOT2) distribution, a typical lipid rafts marker, which again showed marked alterations only in the NPC1 mutant showing major trafficking delay. Finally, treatment with N-butyldeoxynojirimycin (NB-DNJ, Miglustat) led to a reduction of stored lipids in cells from both patients to various extents, however, no normalisation in lipid raft structure was achieved. The data presented in this study help in understanding the varying biochemical phenotypes observed in patients harbouring different mutations, which explain why the effectiveness of NB-DNJ treatment is patient specific.

Molecular dynamics simulation and experimental investigation of furfural separation from aqueous solutions via PEBA-2533 membranes

Abstract Molecular dynamics (MD) simulation was adopted to study the feed-membrane surface affinity and transport behavior of furfural molecules when a poly(ether block amide) (PEBA-2533) membrane was employed. The furfural molecules exhibited a stronger interaction with the PEBA-2533 membrane than the water molecules. Transport behavior analysis indicated that the self-diffusion selectivity in the membrane increased with an increase in feed furfural concentration and the cavity size of the membrane was crucial for the separation of larger molecules. Additionally, the fractional free volume, fractional accessible volume, and fractional cavity volume (FCV) of the PEBA-2533 membrane were analyzed to reveal the variation in membrane structure. Interestingly, the water flux was more sensitive to the variation in membrane thickness than the furfural flux. The permeate furfural concentration increased with an increase in membrane thickness and a membrane selectivity damping model was proposed to explain this phenomenon. The MD technique showed great potential as an approach to characterize the performance of the PEBA-2533 membrane during the pervaporation process.

Forced adhesive growth of K562 leukemic cells that normally grow in suspension induces variations in membrane lipids and energy metabolism: a proton NMR study.

The mechanisms responsible for the adhesion of cells onto a material's surface and the effects that that adhesion may have on cell structure and function are fundamental questions in biomaterials research. We recently demonstrated that the erythroleukemic cell line K562, which normally grows in suspension, can be induced to grow attached to a polylysine-coated solid surface in an anchorage-dependent manner. In this study, the effects of the growth of K562 cells onto polylysine were further investigated utilizing 500 MHz 1H-NMR spectroscopy. The NMR results showed that when K562 cells are grown attached to a positively-charged polylysine surface, there are alterations in lipids and energy metabolism. In particular, there was a 31% increase in phosphatidylcholine and a 15% decrease in each of its two precursors, glycerophosphatidylcholine and choline, as well as a 20% increase in CH2 lipids and a 7% decrease in CH3 lipids in treated cells compared to the controls. These results suggest that adhesive growth can induce strong variations in membrane structure, including the membrane fluidity of K562 cells. In addition, in cells attached to polylysine there was about a 10% decrease in creatine (together with phosphocreatine), a 20% increase in gamma-glutamate, a 15% increase in beta-glutamate, and a 24% decrease in lactate. This second set of results, which is closely related to energy metabolism, indicates that not only does adhesive growth induce changes in K562 cell membrane structure, but also in the utilization of energy in these cells. The data are discussed in view of the possible role played by surface charge in affecting cell structure and function in cells that come into direct contact with charged biopolymers.

The effect of papulacandin B on (1→3)-β- d-glucan synthetases. A possible relationship between inhibition and enzyme conformation

The antibiotic, papulacandin B, inhibited growth or (1→3)-β- d-glucan synthetase (or both) in the fungi Saccharomyces cerevisiae, Hansenula anomala, Neurospora crassa, Cryptococcus laurentii, Schizophyllum commune and Wangiella dermatitidis. No efect was observed on Achlya ambisexualis. There was no apparent correlation between the inhibition of growth and that of the synthetase. With most of the fungal extracts, the inhibition of glucan synthetase by papulacandin B became less pronounced as the substrate (UDP-glucose) concentration was decreased. At very low levels of UDP-glucose, with the enzymes from S. cerevisiae and W. dermatitidis, the antibiotic stimulated the activity of glucan synthetase. As further studied with the W. dermatitidis enzyme, those low concentrations of UDP-glucose corresponded to a sigmoidal portion of the rate vs. substrate curve. The sigmoid segment of the curve extended to higher concentrations of UDP-glucose as the temperature was increased. Concomitantly, the range of substrate concentrations at which papulacandin B stimulated the reaction or was noninhibitory was broadened. It is tentatively concluded that glucan synthetase may exist in more than one interconvertible form. The stimulatory effect of papulacandin B is possibly due to preferential binding to the active form of the enzyme. The equilibrium between these forms could be shifted by structural changes in the membrane in which the enzyme is embedded. The lack of correlation between the effects of papulacandin B in whole cells and in extracts is discussed in terms of the variations in membrane structure in the two situations.

Book reviewFundamental Aspects of Metastasis. Edited by WeissLeonard, pp. xix + 443, 1976 (North-Holland Publishing Company, Amsterdam – Oxford), $53.95.

This book, an expanded version of papers presented at a meeting in Buffalo last July, has appeared with commendable speed; and it covers much of the ground implied in its title. A good deal of attention is devoted to biophysical changes in the surface of neoplastic cells, but it is clear that the appraisal of such changes is still immensely difficult. What, for example, is their specificity? And how do they actually contribute to the phenotypic traits of invasiveness and metastasis? Subtle variations in membrane structure rather than gross abnormalities seem to be involved, and current investigations appear to be moving towards the study of topographical redistribution components in and on the cell surface.

Moving Molecules across Membranes

The transmission of nerve pulses coupled to a process known as active transport-the movement of sodium and potassium ions across cell membranes. Disruption of the balance between calcium and magnesium ions in heart cell membranes can cause the heart to stop beating. Kidney function and the excretion of waste products from the body depend upon the active transport of sodium and potassium ions in kidney membranes. Indeed, the active transport of various chemical ions in membranes vital to maintaining the internal environment of virtually all cells, and maintaining that internal milieu essential to normal biochemical activity. Active transport, however, not among the most well known of biological phenomena; nor it one that particularly well understood. of the central unsolved problems of biology, says Dr. David E. Green, codirector of the Institute for Enzyme Research of the University of Wisconsin, is the mechanism by which ions are actively transported across cell membranes and concentrated in the interior spaces. With two colleagues, Drs. John H. Young and George A. Blondin, Dr. Green proposes a new theory to explain that mechanism. Discussed briefly at the recent meeting of the National Academy of Sciences (SN: 5/9, p. 459), details were presented at a June meeting on the chemistry of natural products in Riga, U.S.S.R. One of the predominant theories of active transport that cell membranes contain a protein that somehow acts as a pump, moving ions against a chemical gradient as if it were pushing water uphill from a low-level reservoir to a higher one. But that theory supported more by speculation than by experimental evidence. From experiments with mitochondria, the energy-producing storehouses of cells, Dr. Green has evidence that disputes the pump theory, replacing it with what he calls a conformational model of active transport. His theory suggests that ions, instead of being pumped uphill, flow smoothly through membranes because of conformational changes in the structure of the membranes themselves. In other words, cyclic variations in membrane structure, in effect, raise the lower reservoir to the level of the higher one, allowing ions to move freely down an electrochemical potential gradient rather than against it. Mitochondrial membranes are built of dumbbell-shaped repeating units of lipids and proteins. According to the conformational model, units of the inner membrane synchronously undergo a cycle of being energized and de-energized. In this cyclic process, the membrane architecture changes. During the energized phase, the lipoprotein repeating units expose binding sites that, like a magnet, pull negatively charged ions such as inorganic phosphate or acetate to them. At the same time, positively charged counter ions move in to neutralize the energy state. Development of the conformational model of active transport depended upon two prior discoveries. One was understanding of energy transduction in mitochondria. The other was isolation and characterization this year of molecules called ionophores within mitochondrial membranes. Ordinarily, Dr. Green explains, you cannot have a charged molecule through a lipid But Dr. Blondin, with Dr. Robert M. Hull, also of Wisconsin University, found that ionophores are vehicles that can get them through. They are doughnutshaped carriers that enclose potassium or sodium ions within their centers and transport them through the membrane. lonophores, in addition, are ion-specific. Thus, the concentration of potassium-receptive ionophores within a membrane, for example, plays a role in determining the quantities of potassium versus sodium ions that can get through. In individual mitochondrial membranes, these molecules are present in extremely small quantities. Those that were isolated by the Wisconsin scientists came from beef hearts, supplied in almost unlimited quantity by a Madison packinghouse. Having determined the method by which ions are transported across membranes, Dr. Green and his colleagues went on to show that they are held inside the mitochondria by an electrochemical potential gradient established by the conformational change. In the de-energized phase, ions are released and the cycle begins again. The key remaining question whether the conformational model established from these experiments with mitochondria will hold for active transPhotos: Univ. of Wis.

Variation in membrane structure as revealed by negative staining technique

A study has been made of the structure of membrane material from various fractions of cellular homogenates. By the use of the negative staining technique several types of membrane structure have been observed. The variation occurs in both internal structure and in the surface features of the different membrane types. The structures observed are characteristic of different membrane fractions and are reproducible under the conditions described. We propose that the structures observed in response to the negative staining technique represent characteristic structural or chemical properties of each type of membrane and are therefore a clue to significant differences in the natural membrane structures, although the structures observed may not exist in the same configuration within the cell.