Affinity precipitation of an antibody by ligand-modified phospholipids

A new method for the selective precipitation of proteins is applied to the isolation and purification of an antibody. Ligand-modified phospholipids (LMPs) are solubilized by the nonionic ethoxylated alcohol detergent, resulting in small (50 to 100 A) micellar aggregates of LMPs and surfactant. When introduced into protein solutions containing an antibody for which the LMP has specific affinity, the ligand binds to the protein. Hydrophobic interactions between phospholipid tail groups bound to the protein molecules result in an insoluble precipitate. Polyclonal and monoclonal antibiotin antibody (pABA and mABA) are shown to be selectively precipitated using ratios of dimyristoylphosphatidylethanolamidobiotin (DMPE-B) to ABA ranging from 1:1 to 19:1. The kinetics and yield of the precipitation achieve a maximum at a ratio of DMPE-B to ABA of approximately 7:1. The kinetics and magnitude of the turbidity change are modeled using the Mie theory of light scattering coupled with the smoluchowski theory of aggregation. The kinetics are shown to be enhanced significantly by the addition of salt. In particular, the addition of 0.5 M ammonium sulfate salt increases the rate of precipitation by more than an order of magnitude. It is demonstrated that pABA can be recovered with total activity yields of 60% to 70% from mixtures containing nonspecific lgG antibodies in very high purity (>99%). (c) 1994 John Wiley & Sons, Inc.     

Molecular weights of alpha beta-protomeric and oligomeric units of soluble (Na+, K+)-ATPase determined by low-angle laser light scattering after high-performance gel chromatography

The (Na+, K+)-ATPase of canine renal outer medulla was solubilized with a nonionic surfactant, octaethylene glycol n-dodecyl ether (C12E8), in the presence of 0.2 M sodium ion. The solubilized ATPase retained 74% of the enzymatic activity expressed before solubilization. Molecular species of the solubilized ATPase were analyzed by high-performance chromatography through a TSK-GEL G3000SW column in the presence of 1 mg/ml C12E8 at 23 degrees C. The eluate was monitored by one or two monitors chosen from the following: an ultraviolet absorption monitor, a precision differential refractometer and a low-angle laser light scattering photometer. The three kinds of elution pattern thus obtained can best be interpreted by assuming the presence of at least four kinds of protein component with molecular weights 1 740 000 +/- 230 000, 836 000 +/- 82 000, 286 000 +/- 30 000 and 123 000 +/- 8 000, respectively. Among them, those with the last two molecular weight were the major components. The amounts of the first three components were found to increase with time during the incubation before application to the column at the expense of that of the last one. The amounts of the last two were 18 and 73%, respectively, when measured immediately after the solubilization. A stoichiometric composition of 1:1 molar ratio for the alpha and beta polypeptide chains was obtained for the two major components as well as for the intact ATPase by high-performance gel chromatography in the presence of sodium dodecyl sulfate using the same column as above. The (Na+, K+)-ATPase was, thus, indicated to be solubilized with C12E8 to give the alpha beta-protomer and its dimer as the main components.     

Biodegradation of naphthalene in aqueous nonionic surfactant systems.

The principal objective of this study was to quantify the bioavailability of micelle-solubilized naphthalene to naphthalene-degrading microorganisms comprising a mixed population isolated from contaminated waste and soils. Two nonionic surfactants were used, an alkylethoxylate, Brij 30 (C12E4), and an alkylphenol ethoxylate, Triton X-100 (C8PE9.5). Batch experiments were used to evaluate the effects of aqueous, micellized nonionic surfactants on the microbial mineralization of naphthalene and salicylic acid, an intermediate compound formed in the pathway of microbial degradation of naphthalene. The extent of solubilization and biodegradation under aerobic conditions was monitored by radiotracer and spectrophotometric techniques. Experimental results showed that surfactant concentrations above the critical micelle concentration were not toxic to the naphthalene-degrading bacteria and that the presence of surfactant micelles did not inhibit mineralization of naphthalene. Naphthalene solubilized by micelles of Brij 30 or Triton X-100 in liquid media was bioavailable and degradable by the mixed culture of bacteria.     

Effects of nonionic surfactants on the solubilization and mineralization of phenanthrene in soil-water systems

The solubilization and mineralization of (14)C-phenanthrene in soil-water systems was examined with several commercially available surface-active agents, viz., an alkyl ethoxylate C(12)E(4); two alkylphenol ethoxylate surfactants: C(8)PE(9.5) and C(9)PE(10.5); two sorbitan ethoxylate surfactants: the sorbitan monolaurate (Tween 20) and the sorbitan monooleate (Tween 80); two pairs of nonionic ethoxylate surfactant mixtures: C(12)E(4)/C(12)E(23) at a 1:1 ratio, and C(12-15)E(3)/C(12-15)E(9) at a 1:3 ratio; and two surfactants possessing relatively high critical micelle concentration (CMC) values and low aggregation numbers: CHAPS and octyglucoside. Surface tension experiments were performed to evaluate surfactant sorption onto soil and the surfactant doses required to attain the CMC in the soil-water systems. Surfactant solubilization of (14)C-phenanthrene commenced with the onset of micellization. The addition of surface-active agents was observed not to be beneficial to the microbial mineralization of phenanthrene in the soil-water systems and, for supra-CMC surfactant doses, phenanthrene mineralization was completely inhibited for all the surfactants tested. A comparison of solubilization, surface tension, and mineralization data confirms that the inhibitory effect on microbial degradation of phenanthrene is related to the CMC of the surfactant in the presence of soil. Additional tests demonstrated the recovery of mineralization upon dilution of surfactant concentration to sub-CMC levels, and a relatively high exit rate for phenanthrene from micelles. These tests suggest that the inhibitory effect is probably related to a reversible physiological surfactant micelle-bacteria interaction, possibly through partial complexing or release of membrane material with disrupting membrane lamellar structure. This study indicates that nonionic surfactant solubilization of sorbed hydrophobic organic compounds from soil may not be beneficial for the concomitant enhancement of soil bioremediation. Additional work is needed to address physicochemical processes for bioavailability enhancement, and effects of solubilizing agents on microorganisms for remediation and treatment of hydrophobic organic compounds and nonaqueous phase liquids. (c) 1992 John Wiley & Sons Inc.     

Role of surfactant on the proteolysis of aqueous bovine serum albumin

Nonionic and ionic surfactants diminish the initial rate of proteolysis of aqueous bovine serum albumin (BSA) by subtilisin Carlsberg. Surfactants studied include: nonionic tetraethylene glycol monododecyl ether (C12E4); anionic sodium dodecyl sulfate (SDS), anionic sodium dodecylbenzenesulfonate (SDBS), and cationic dodecyltrimethylamonium bromide (DTAB). Kinetic data are obtained using fluorescence emission. Special attention is given to enzyme kinetic specificity determined by fitting initial-rate data to the Michaelis-Menten model. All surfactants reduce the rate of proteolysis, most strongly at concentrations near and above the critical micelle concentration (CMC). Circular dichroism (CD), tryptophan/tyrosine fluorescence spectra, and tryptophan fluorescence thermograms indicate that BSA partially unfolds at ionic surfactant concentrations near and above the CMC. Changes in BSA conformation are less apparent at ionic surfactant concentrations below the CMC and for the nonionic surfactant C12E4. Subtilisin Carlsberg activity against the polypeptide, succinyl-Ala-Ala-Pro-Phe-p-nitroanilide, decreased due to enzyme-surfactant interaction. At the concentrations and time frames studied, there was no enzyme autolysis. Importantly, aqueous proteolysis rates are significantly reduced at high surfactant concentrations where protein-micellar-surfactant aggregates occur. To explain the negative effect of surfactant on subtilisin Carlsberg proteolytic activity against BSA, we propose that micelle/protein complexes hinder enzyme access.     

Investigation on the mechanism of crystallization of soluble protein in the presence of nonionic surfactant

The mechanism of crystallization of soluble, globular protein (lysozyme) in the presence of nonionic surfactant C8E4 (tetraoxyethylene glycol monooctyl ether) was examined using both static and dynamic light scattering. The interprotein interaction was found to be attractive in solution conditions that yielded crystals and repulsive in the noncrystallizing solution conditions. The validity of the second virial coefficient as a criterion for predicting protein crystallization could be established even in the presence of nonionic surfactants. Our experiments indicate that the origin of the change in interactions can be attributed to the adsorption of nonionic surfactant monomers on soluble proteins, which is generally assumed to be the case with only membrane proteins. This adsorption screens the hydrophobic attractive force and enhances the hydration and electrostatic repulsive forces between protein molecules. Thus at low surfactant concentration, the effective protein-protein interaction remains repulsive. Large surfactant concentrations promote protein crystallization, possibly due to the attractive depletion force caused by the intervening free surfactant micelles.     

The state of association of band 3 protein of the human erythrocyte membrane in solutions of nonionic detergents

Band 3 protein, the anion transport protein of the human erythrocyte membrane, was solubilized and purified in aqueous solutions of two nonionic detergents: Ammonyx-LO (dimethyl laurylamine oxide) and C12E9 (nonaethylene glycol lauryl ether). The state of association of the purified protein was studied by analytical ultracentrifugation. Band 3 protein solubilized and studied in solutions of Ammonyx-LO was found to be in a monomer/dimer/tetramer association equilibrium. Band 3 protein freshly prepared in C12 E9 showed the same behaviour; however, during aging the protein was converted into stable noncovalent dimers. The conversion was retarded by the presence of beta-mercaptoethanol or by treatment of the samples with iodoacetamide; it seems to be due to oxidation of the protein by degradation products of the detergent. It is concluded that a monomer/dimer/tetramer association equilibrium is the native state of association of band 3 protein solubilized by nonionic detergents. Since nonionic detergents are assumed not to interfere with protein-protein interactions among membrane proteins, the results strongly support the claim that, in the erythrocyte membrane, band 3 is in a monomer/dimer/tetramer association equilibrium (Dorst, H.-J. and Schubert, D. (1979) Hoppe-Seyler's Z. Physiol. Chem. 360, 1605-1618).     

Membrane solubilization by detergent: use of brominated phospholipids to evaluate the detergent-induced changes in Ca2+-ATPase/lipid interaction

The solubilization and delipidation of sarcoplasmic reticulum Ca2+-ATPase by different nonionic detergents were measured from changes in turbidity and recovery of intrinsic fluorescence of reconstituted ATPase in which tryptophan residues had been quenched by replacement of endogenous phospholipids with brominated phospholipids. It was found that incorporation of C12E8 or dodecyl maltoside (DM) at low concentrations in the membrane, resulting in membrane "perturbation" without solubilization, displaced a few of the phospholipids in contact with the protein; perturbation was evidenced by a parallel drop in ATPase activity. As a result of further detergent addition leading to solubilization, the tendency toward delipidation of the immediate environment of the protein was stopped, and recovery of enzyme activity was observed, suggesting reorganization of phospholipid and detergent molecules in the solubilized ternary complex, as compared to the perturbed membrane. After further additions of C12E8 or DM to the already solubilized membrane, the protein again experienced progressive delipidation which was only completed at a detergent concentration about 100-fold higher than that necessary for solubilization. Delipidation was correlated with a decrease in enzyme activity toward a level similar to that observed during perturbation. On the other hand, Tween 80, Tween 20, and Lubrol WX failed to solubilize SR membranes and to induce further ATPase delipidation when added after preliminary SR solubilization by C12E8 or dodecyl maltoside. For Tween 80, this can be related to an inability to solubilize pure lipid membrane; in contrast, Tween 20 and Lubrol WX were able to solubilize liposomes but not efficiently to solubilize SR membranes. In all three cases, insertion of the detergent in SR membranes is, however, demonstrated by perturbation of enzyme activity. Correlation between detergent structure and ability to solubilize and delipidate the ATPase suggests that one parameter impeding ATPase solubilization might be the presence of a bulky detergent polar headgroup, which could not fit close to the protein surface. We also conclude that in the active protein/detergent/lipid ternary complexes, solubilized by C12E8 or dodecyl maltoside, most phospholipids remain closely associated with the ATPase hydrophobic surface as in the membranous form. Binding of only a few detergent molecules on this hydrophobic surface may be sufficient for inhibition of ATPase activity observed at high ATP concentration, both during perturbation and in the completely delipidated, solubilized protein.(ABSTRACT TRUNCATED AT 400 WORDS)     

Binding, activation, and solubilization of the Ca2+-ATPase from sarcoplasmic reticulum by nonionic detergents

Interactions between delipidated Ca2+-ATPase from sarcoplasmic reticulum and four nonionic detergents--dodecyl octaoxyethyleneglycol monoether (C12E8), Triton X-100, Brij 58, and Brij 35--were characterized with respect to activation of ATPase activity, binding, and solubilization. C12E8 and Triton X-100 activated the delipidated ATPase to at least 80% of the original activity at the critical micelle concentrations (CMCs), whereas Brij 58 and Brij 35 activated no more than 10% of the original activity. The inability of Brij 58 and Brij 35 to activate the delipidated enzyme was probably a result of reduced binding of these detergents below the CMCs; both detergents exhibited a sixteenfold reduction in binding at the CMC compared with C12E8. The two Brij detergents were also unable to solubilize the delipidated enzyme and form monomers, as determined by sedimentation experiments. Thus the reduced binding levels of these detergents may result from an inability to overcome protein/protein interactions in the delipidated preparation. However, the Brij detergents were capable of solubilizing active enzyme from membrane vesicles, although with lower efficiency than C12E8 and Triton X-100. These results suggest that Brij 58 and 35 may be useful for solubilization of membrane proteins without disrupting protein/protein interactions, while Triton X-100 and C12E8 are more useful when bulk solubilization is the goal.     

Solubilization and reconstitution of membrane proteins of Escherichia coli using alkanoyl-N-methylglucamides

Alkanoyl-N-methylglucamides, nonionic detergents, were utilized to solubilize membrane proteins of Escherichia coli and were used to reconstitute them into liposomes. First, critical micelle concentrations (CMC) of nonanoyl-N-methylglucamide and decanoyl-N-methylglucamide were determined to be 25 mM and 7 mM, respectively, by photometric assay. Then solubilization and reconstitution of the melibiose transport carrier were performed using these detergents at concentrations above the CMC. Melibiose counterflow activity was observed with the proteoliposomes reconstituted from the extracted proteins and phospholipids. The proton-translocating ATPase complex (F1-F0) was also solubilized with these detergents. These results indicate that nonanoyl- and decanoyl-N-methylglucamide are useful detergents for solubilization and reconstitution of membrane proteins.     

Solubilization and reconstitution of vesicular stomatitis virus envelope using octylglucoside.

Reconstituted vesicular stomatitis virus envelopes or virosomes are formed by detergent removal from solubilized intact virus. We have monitored the solubilization process of the intact vesicular stomatitis virus by the nonionic surfactant octylglucoside at various initial virus concentrations by employing turbidity measurements. This allowed us to determine the phase boundaries between the membrane and the mixed micelles domains. We have also characterized the lipid and protein content of the solubilized material and of the reconstituted envelope. Both G and M proteins and all of the lipids of the envelope were extracted by octylglucoside and recovered in the reconstituted envelope. Fusion activity of the virosomes tested either on Vero cells or on liposomes showed kinetics and pH dependence similar to those of the intact virus.     

Mesoscopic simulation of cell membrane damage, morphology change and rupture by nonionic surfactants.

A new simulation method, dissipative particle dynamics, is applied to model biological membranes. In this method, several atoms are united into a single simulation particle. The solubility and compressibility of the various liquid components are reproduced by the simulation model. When applied to a bilayer of phosphatidylethanolamine, the membrane structure obtained matches quantitatively with full atomistic simulations and with experiments reported in the literature. The method is applied to investigate the cause of cell death when bacteria are exposed to nonionic surfactants. Mixed bilayers of lipid and nonionic surfactant were studied, and the diffusion of water through the bilayer was monitored. Small transient holes are seen to appear at 40% mole-fraction C(9)E(8), which become permanent holes between 60 and 70% surfactant. When C(12)E(6) is applied, permanent holes only arise at 90% mole-fraction surfactant. Some simulations have been carried out to determine the rupture properties of mixed bilayers of phosphatidylethanolamine and C(12)E(6). These simulations indicate that the area of a pure lipid bilayer can be increased by a factor 2. The inclusion of surfactant considerably reduces both the extensibility and the maximum stress that the bilayer can withstand. This may explain why dividing cells are more at risk than static cells.     

Effect of a commercial alcohol ethoxylate surfactant (C<Subscript>11-15</Subscript>E<Subscript>7</Subscript>) on

Biodegradation of poorly soluble polycyclic aromatic hydrocarbons (PAHs) has been a challenge in bioremediation. In recent years, surfactant-enhanced bioremediation of PAH contaminants has attracted great attention in research. In this study, biodegradation of phenanthrene as a model PAHs solubilized in saline micellar solutions of a biodegradable commercial alcohol ethoxylate nonionic surfactant was investigated. The critical micelle concentration (CMC) of the surfactant and its solubilization capacity for phenanthrene were examined in an artificial saline water medium, and a type of marine bacteria, Neptunomonas naphthovorans, was studied for the biodegradation of phenanthrene solubilized in the surfactant micellar solutions of the saline medium. It is found that the solubility of phenanthrene in the surfactant micellar solutions increased linearly with the surfactant concentrations, but, at a fixed phenanthrene concentration, the biodegradability of phenanthrene in the micellar solutions decreased with the increase of the surfactant concentrations. This was attributed to the reduced bioavailability of phenanthrene, due to its increased solubilization extent in the micellar phase and possibly lowered mass transfer rate from the micellar phase into the aqueous phase or into the bacterial cells. In addition, an inhibitory effect of the surfactant on the bacterial growth at high surfactant concentrations may also play a role. It is concluded that the surfactant largely enhanced the solubilization of phenanthrene in the saline water medium, but excess existence of the surfactant in the medium should be minimized or avoided for the biodegradation of phenanthrene by Neptunomonas naphthovorans.     

Determination of molecular weight of membrane proteins by the use of low-angle laser light scattering combined with high-performance gel chromatography in the presence of a non-ionic surfactant

An assessment study was carried out to evaluate the performance of the low-angle laser light scattering technique combined with high-performance gel chromatography in the presence of a nonionic surfactant, octaethyleneglycol n-dodecyl ether, precision differential refractometry and ultraviolet photometry. It was found that the combined technique is highly promising as a method for the determination of the molecular weight of a membrane protein solubilized by the surfactant. For trial, molecular weights of the following membrane proteins of Escherichia coli, both solubilized in oligomeric forms, were measured; porin that forms the transmembrane diffusion pore in the outer membrane, and lambda-receptor protein that facilitates the diffusion of maltose-maltodextrins across the outer membrane. The result obtained indicates that both porin and lambda-receptor protein exist as trimers in the surfactant solution.     

Assessing bioavailability of the solubilization of organic compound in nonionic surfactant micelles by dose–response analysis

It is uncertain in some extent that organic compounds solubilized in micelles of a nonionic surfactant aqueous solution are bioavailable directly by the microbes in an extractive microbial transformation or biodegradation process. In this work, a dose–response method, where a bioequivalence concept is introduced to evaluate the synergic toxicity of the nonionic surfactants and the organic compounds, was applied to analyze the inhibition effect of organic compounds (naphthalene, phenyl ether, 2-phenylethanol, and 1-butanol) in nonionic surfactant Triton X-100 micelle aqueous solutions and Triton X-114 in aqueous solutions forming cloud point systems. Based on the result, a mole solubilization ratio of organic compounds in micelle was also determined, which consisted very well with those of classic semi-equilibrium dialysis experiments. The results exhibit that bioavailability of organic compounds solubilized in micelles to microbial cells is negligible, which provides a guideline for application of nonionic surfactant micelle aqueous solutions or cloud point systems as novel media for microbial transformations or biodegradations.     

Properties of oligomycin-induced occlusion of Na+ by detergent-solubilized Na,K-ATPase from pig kidney or shark rectal gland.

Oligomycin induces occlusion of Na+ in membrane-bound Na,K-ATPase. Here it is shown that Na,K-ATPase from pig kidney or shark rectal gland solubilized in the nonionic detergent C12E8 is capable of occluding Na+ in the presence of oligomycin. The apparent affinity for Na+ is reduced for both enzymes upon solubilization, and there is an increase in the sigmoidicity of binding curves, which indicates a change in the cooperativity between the occluded ions. A high detergent/protein ratio leads to a decreased occlusion capacity. De-occlusion of Na+ by addition of K+ is slow for solubilized Na,K-ATPase, with a rate constant of about 0.1 s-1 at 6 degrees C. Stopped-flow fluorescence experiments with 6-carboxyeosin, which can be used to monitor the E1Na-form in detergent solution, show that the K(+)-induced de-occlusion of Na+ correlates well with the fluorescence decrease which follows the transition from the E1Na-form to the E2-form. There is a marked increase in the rate of fluorescence change at high detergent/protein ratios, indicating that the properties of solubilized enzyme are subject to modification by detergent in other respects than mere solubilization of the membrane-bound enzyme. The temperature dependence of the rate of de-occlusion in the range 2 degrees C to 12 degrees C is changed slightly upon solubilization, with activation energies in the range 20-23 kcal/mol for membrane-bound enzyme, increasing to 26-30 kcal/mol for solubilized enzyme. Titrations of the rate of transition from E1Na to E2K with oligomycin can be interpreted in a model with oligomycin having an apparent dissociation constant of about 2.5 microM for C12E8-solubilized shark Na,K-ATPase and 0.2 microM for solubilized pig kidney Na,K-ATPase.     

Formulation and Characterization of Phytophenol-Carrying Antimicrobial Microemulsions

Phytophenols were solubilized in nonionic surfactant micelles to form antimicrobially active and thermodynamically stable microemulsions. Formulation of phytophenols in microemulsions has previously been shown to improve their antimicrobial activity in model microbiological and food systems. Carvacrol and eugenol were incorporated in micellar solutions of two nonionic surfactants (Surfynol® 485W and Surfynol® 465) by mixing at room temperature. Particle size of formed microemulsions was determined by dynamic light scattering, and structural information about the mixed micellar system was obtained by nuclear magnetic resonance spectroscopy (NMR). Uptake of carvacrol and eugenol in surfactant micelles as determined by ultrasonic velocity measurements was very rapid, e.g., below the maximum additive concentration, the phytophenols were completely solubilized in the micelles in less than 30 min. Depending on the surfactant–phytophenol combination, the self-assembled surfactant–phytophenol aggregates had mean particle diameters between 3 and 17 nm. Elucidation of the structure of aggregates by 1H NMR studies indicated that micelles had a “bracket-like” structure with phytophenols being located inside the palisade layer of the micelle in direct contact with adjacent surfactant monomers. Encapsulation of phytophenols in surfactant micelles enables the incorporation of large amounts of hydrophobic antimicrobials in aqueous phases. Formulation of antimicrobial microemulsions may thus offer a means to deliver high concentrations of phytophenols to the bacterial surfaces of foodborne pathogens to affect kill.     

The lactose permease of Escherichia coli: evidence in favor of a dimer

Lactose permease from Escherichia coli T 206 was purified in octyl-beta-D-glucopyranoside (octyl-glucoside) according to Newman et al. [J. Biol. Chem. (1981) 256, 11804-11808]. In this detergent the protein has a very high tendency to aggregate nonspecifically. Therefore, exchange of octyl-glucoside was performed for another nonionic detergent, dodecyl octaethylene glycol monoether (C12E8), in which the protein is more stable. The amounts of bound C12E8 and phospholipids were measured using radioactive detergent and gas chromatography, respectively, and were found to be respectively 0.2 and 0.15 g/g protein. Analytical ultracentrifugation (sedimentation velocity and sedimentation equilibrium) and gel filtration (conventional and high performance liquid chromatography) experiments indicated that in this detergent the lactose permease existed mainly as a dimer. This result is at variance with the monomeric state of the protein reported by Wright et al. [FEBS Lett. (1983) 162, 11-15] in another nonionic detergent (dodecyl-o-beta-maltoside). We discuss the possible reason for this discrepancy and suggest that the dimeric state of association may well reflect the situation that prevails in the membrane.     

In Situ emulsification and mobilization of gasoline range hydrocarbons using surfactants

In this article the conditions that govern surfactant‐enhanced emulsification and mobilization of petroleum hydrocarbons in soil are reviewed. The effect of soil properties, groundwater constituents, and differing surfactant solutions on the emulsification process is discussed. A constant head soil flushing apparatus used to characterize surfactant‐enhanced mobilization of m‐xylene is described. Data showing the effect of surfactant‐enhanced mobilization on m‐xylene removal efficiency in washed sand is presented. Flushing solutions were used at concentrations from below to well above the critical micelle concentration (CMC) of the surfactants used. Removal efficiencies are shown to vary with surfactant concentration and with surfactant type. Flushing solutions of anionic, nonionic, and anionic/nonionic surfactant mixtures were evaluated.     

On stability of circular hole in membrane bilayer.

It was observed recently that nonionic surfactant octaethyleneglycol dodecylether (Cl2E8) decreases threshold for irreversible electroporation in membrane bilayers. In accordance, it is shown theoretically in this work that anisotropic C12E8 membrane inclusions may stabilize circular hole in a flat membrane segment.