The effect of merulinic acid on biomembranes

Merulinic acid (heptadecenylresorcinolic acid, resorcinolic acid) is one of the members of resorcinolic lipids, the natural amphiphilic long-chain homologues of orcinol (1,3-dihydroksy-5-methylbenzene). In the present study, membrane properties of merulinic acid were investigated. Merulinic acid exhibits strong haemolytic activity against sheep erythrocytes (EH₅₀ of 5±2 μM) regardless of the form of its application—direct injection into the erythrocyte suspension or injection as merulinic acid-enriched liposomes. The lysis of erythrocytes induced by merulinic acid was inhibited by the presence of divalent cations. The effectivity of the protection of erythrocytes was highest for Zn²⁺ and weakest for Mn²⁺.Merulinic acid at low concentrations also exhibits the ability for protection of cells against their lysis in hypoosmotic solutions. This protective effect is significant as, at 10 μM concentration of merulinic acid, the extent of osmotically induced cell lysis is reduced by approximately 40%. Merulinic acid induces increased permeability of liposomal vesicles. This effect was shown to be dependent on the composition of liposomal bilayer and it was stronger when lipid bilayer contained glycolipids (MGDG and DGDG) and sphingomyelin.Changes of TMA-DPH and NBD-PE fluorescence polarization show that the degree of merulinic acid incorporation into liposomal membrane is not very high. The polar “heads” of the molecules of investigated compounds are localized on the level of fatty acid's ester bonds in phospholipid molecules. Merulinic acid caused the increased fluorescence of the membrane potential fragile probe. This indicated an alteration of the surface charge and a decrease of the local pH at the membrane surface. This effect was visible in both low- and high-ionic strength environment. Merulinic acid causes also a decrease in activity of the membrane-bound enzyme acetylcholinesterase.     

The effect of oxidants on biomembranes and cellular metabolism

During the reductive process in the tissues, the aerobes generate a number of oxidants. Unless these oxidants are reduced, oxidative damage and cell death would occur. Oxidation of plasma membrane lipids leads to autocatalytic chain reactions which eventually alter the permeability of the cell. The role of oxidative damage in the pathophysiology of diabetic complications and ischemic reperfusion injury of myocardium, especially the changes in the channel activity which may lead to arrhythmia have been studied. Hyperglycemia activates aldose reductase which could efficiently reduce glucose to sorbitol in the presence of NADPH. Since NADPH is also aldose required by glutathione reductase for reducing oxidants, its diversion would lead to membrane lipid oxidation and permeability changes which are probably responsible for diabetic complications such as cataractogenesis, retinopathy, neuropathy etc. Antioxidants such as butylated hydroxy toluene (BHT) and also reductase inhibitors prevent or delay some of these complications. By using patch-clamp technique in isolated frog myocytes, we have shown that hydroxy radicals generated by ferrous sulfate and ascorbate as well as lipid peroxides such as t-butyl hydroperoxide facilitate the entry of Na⁺ by oxidizing Na⁺-channels. Increased intracellular Na⁺ leads to an increase in Na⁺/Ca²⁺ exchange. The increased Na⁺ concentration by itself may produce electrical disturbance which would result in arrhythmia. Increased Ca²⁺ may affect proteases and may help in the conversion of xanthine dehydrogenase to xanthine oxidase, consequently increased production of super oxide radicals. Increased membrane lipid peroxidation and other oxygen free-radical associated membrane damage in myocytes has been demonstrated.     

Exploring hydrophobic sites in proteins with xenon or krypton

X-ray diffraction is used to study the binding of xenon and krypton to a variety of crystallised proteins: porcine pancreatic elastase; subtilisin Carlsberg from Bacillus licheniformis; cutinase from Fusarium solani; collagenase from Hypoderma lineatum; hen egg lysozyme, the lipoamide dehydrogenase domain from the outer membrane protein P64k from Neisseria meningitidis; urate-oxidase from Aspergillus flavus, mosquitocidal δ-endotoxin CytB from Bacillus thuringiensis and the ligand-binding domain of the human nuclear retinoid-X receptor RXR-α. Under gas pressures ranging from 8 to 20 bar, xenon is able to bind to discrete sites in hydrophobic cavities, ligand and substrate binding pockets, and into the pore of channel-like structures. These xenon complexes can be used to map hydrophobic sites in proteins, or as heavy-atom derivatives in the isomorphous replacement method of structure determination. Proteins 30:61–73, 1998. © 1998 Wiley-Liss, Inc.     

Exploring the effect of the Cardinium endosymbiont on spiders

Spiders have recently emerged as important diversity hot spots for endosymbiotic bacteria, but the consequences of these symbiotic interactions are largely unknown. In this article, we examined the evolutionary history and effect of the intracellular bacterium Cardinium hertigii in the marbled cellar spider Holocnemus pluchei. We showed that Cardinium infection is primarily transmitted in spider populations maternally via egg cytoplasm, with 100% of the progeny from infected mothers being also infected. Examination of a co‐inherited marker, mitochondrial DNA (mtDNA), revealed that Cardinium infection is associated with a wide diversity of mtDNA haplotypes, showing that the interaction between Cardinium and H. pluchei has a long‐term evolutionary dimension and that horizontal transmission among individuals could also occur. Although Cardinium is well known to exert sex ratio distortion or cytoplasmic incompatibility in various arthropod hosts, we show, however, that Cardinium does not interact with the reproductive biology of H. pluchei. A field survey shows a clear geographical structuring of Cardinium infection, with a marked gradual variation of infection frequencies from ca. 0.80 to 0. We discuss different mechanistic and evolutionary explanations for these results as well as their consequences for spider phenotypes. Notably, we suggest that Cardinium can either behave as a neutral cytoplasmic element within H. pluchei or exhibit a context‐dependent effect, depending on the environmental conditions.     

Lipid phase transitions in model biomembranes: The effect of ions on phosphatidylcholine bilayers

Differential scanning calorimetry has been used to study the endothermic phase behaviour of some model biomembranes (i.e. phosphatidylcholine-water systems) in the presence of a wide range of alkaline, alkaline earth and heavy metal salts. Studies and comparisons were made of both cation and anion effects. Shifts occur in the temperatures of both the pre-transition and main transition endotherms. The observed shifts are smaller than those which have been reported for charged lipids, and no evidence has been found for the formation of specific complexes. Electron microscopic studies on freeze-fractured dispersions of phosphatidylcholine-water-salt systems show that with some salts the typical rippled surface observed with l-α-dimyristoyl phosphatidylcholine, when in the gel state, is replaced by a smooth surface.     

Theoretical mimicry of biomembranes

The study of membrane proteins requires a proper consideration of the specific environment provided by the biomembrane. The compositional complexity of this environment poses great challenges to all experimental and theoretical approaches. In this article a rather simple theoretical concept is discussed for its ability to mimic the biomembrane. The biomembrane is approximated by three mimicry solvents forming individual continuum layers of characteristic physical properties. Several specific structural problems are studied with a focus on the biological significance of such an approach. Our results support the general perception that the biomembrane is crucial for correct positioning and embedding of its constituents. The described model provides a semi-quantitative tool of potential interest to many problems in structural membrane biology.     

The basic property of biomembranes

In order to explain the experimentally obtained results with biomembranes it has been assumed, that the diameter of all vesicles, defined by a lipid bilayer, form a perfect crystal. Later on it appeared that biomembranes are liquid crystals. Nevertheless already with biomembranes as crystals it was possible to calculate the diameters of all existing vesicles. As shown in the present paper, the results with liquid crystals were identical to those with a perfect crystal-model. Here I demonstrate that the geometric progression of the diameters of vesicles of biomembranes is based on the entropy of the lipids and it is shown that the diameters of biomembranes fit four geometric series. The surface areas of these series of biomembranes can be approximated by the two geometric series published previously. The experiments and the theoretical studies on which this work is based have been carried out at the Netherlands Cancer Institute, Amsterdam, The Netherlands.     

Interaction of staphylococcal alpha-toxin with biomembranes

The recent data on staphylococcal alpha-toxin, its functions, methods for its purification, forms are presented in the review. The problem of a target for toxin molecule is discussed.     

Exploring the effect of confinement on water clusters in carbon nanotubes

Using armchair-type single-walled carbon nanotubes (SWCNTs) of different sizes as model compounds for lignite, the effect of water molecule confinement on the water-holding capacity of lignite pores was investigated. Results indicated that the water-holding capacity of pores with diameters of <10 nm was eight times larger than that of pores with diameters of 100 nm. The configuration of the cluster of water molecules in each SWCNT and the binding energy between each SWCNT and the water molecules within it were calculated by means of density functional theory using a hybrid functional: M06-2X/6-311+G**, 6-31G*. The results prove that the configurations of the water molecules in the SWCNTs are very different to their configuration in the unconfined state. In vacuum, the cluster of three water molecules adopted a trimer configuration, while they presented a linear configuration in the 6.78 Å SWCNT. Similarly, in vacuum, the cluster of five water molecules formed a five-membered ring, while they favored a linear configuration in the 6.78 Å SWCNT, a zigzag configuration in the 8.14 Å SWCNT, and a trimer?+?1?+?1 configuration (i.e., a trimer plus two isolated water molecules) in the 9.49 Å, 10.85 Å, and 13.75 Å SWCNTs. There was found to be a degree of competition between the coupling energy of the water molecules with the SWCNT and the hydrogen bonding among the water molecules. When the diameter of the SWCNT was >1 nm, the hydrogen bonding among the water molecules dominated, while the coupling energy of the water molecules with the SWCNT amounted to only 30–40% of the total interaction energy of the water molecules.

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Graphical Abstract Computed equilibrium structures of five water molecules confined in SWCNTs with diameters of 6.78 Å, 8.14 Å, 9.49 Å, 10.85 Å, and 13.75 Å, and in vacuum

     

Anesthetic Gases and Water Structure : The effect of xenon on tritiated water flux across the gut

Pauling and Miller have independently proposed that the presence of an anesthetic gas in tissue induces a cage-like arrangement of hydrogen-bonded water molecules. The theories recognize that most gas-hydrate crystals would not form at the temperature and pressure that exist during anesthesia and propose that other components of tissue such as protein should have a stabilizing effect. Measurements of the behavior of water, rather than the anesthetic agent, would provide alternative information about the likelihood of hydrate crystal formation and this information could be such as to be applicable to body temperature and to pressures used for anesthesia. If the number of hydrogen-bonded water molecules in tissue is increased, then the movement of an average water molecule should be hindered. Movement of water through the tissue may be measured by tagging it with tritium and the anesthetic gas should then slow the movement of tritiated water through the tissue. The flux of tritiated water through rat cecum is indeed slowed when the cecum is exposed to the anesthetic gas, xenon, which can participate biochemically only by virtue of its van der Waals interaction. The decrement in water flux is in reasonable agreement with what could be expected theoretically from calculations based on the activation energy for the self-diffusion of water and the degree of hypothermia necessary to produce narcosis.     

Exploring the effect of oxygen-containing functional groups on the water-holding capacity of lignite

Graphene oxide with different degrees of oxidation was prepared and selected as a model compound of lignite to study quantitatively, using both experiment and theoretical calculation methods, the effect on water-holding capacity of oxygen-containing functional groups. The experimental results showed that graphite can be oxidized, and forms epoxy groups most easily, followed by hydroxyl and carboxyl groups. The prepared graphene oxide forms a membrane-state as a single layer structure, with an irregular surface. The water-holding capacity of lignite increased with the content of oxygen-containing functional groups. The influence on the configuration of water molecule clusters and binding energy of water molecules of different oxygen-containing functional groups was calculated by density functional theory. The calculation results indicated that the configuration of water molecule clusters was totally changed by oxygen-containing functional groups. The order of binding energy produced by oxygen-containing functional groups and water molecules was as follows: carboxyl > edge phenol hydroxyl >epoxy group. Finally, it can be concluded that the potential to form more hydrogen bonds is the key factor influencing the interaction energy between model compounds and water molecules.     

Interaction of wasp venom mastoparan with biomembranes

Mastoparan-induced changes in the K+ permeability of rat peritoneal mast cells, human erythrocytes, Staphylococcus aureus and Escherichia coli were examined. Mastoparan did not efficiently increase the K+ permeability of cells except for S. aureus. The release of membrane phospholipids was also observed from S. aureus cells in the concentration range of the permeability enhancement. Mastoparan stimulated histamine release from mast cells, independently of a small efflux of K+. Mastoparan became markedly effective to E. coli cells whose outer membrane structure was chemically disrupted beforehand, showing that the peptide can enhance the permeability of the cytoplasmic membranes of both Gram-positive and -negative bacteria. In experiments using liposomes, mastoparan increased the permeability of the liposomes composed of egg phosphatidylethanolamine and egg phosphatidylglycerol, which are the lipid constituents of the cytoplasmic membrane of E. coli cells, while it showed a weak activity to the liposomes composed of egg phosphatidylcholine and cholesterol. The latter result related closely to the fact that this peptide acted weakly on erythrocytes and mast cells in which acidic lipids constitute a minor portion. Mastoparan decreased the phase transition temperature of dipalmitoylphosphatidylglycerol liposomes, but it did not affect that of dipalmitoylphosphatidylcholine liposomes. These results indicate that mastoparan penetrated into membranes mainly containing acidic phospholipids and disrupted the membrane structure to increase the permeability. The action of the wasp venom mastoparan was compared with that of a bee venom melittin.