Bifunctional Membrane Research Articles

When, how and why? Regulated proteolysis by the essential FtsH protease in Escherichia coli.

Cellular proteomes are dynamic and adjusted to permanently changing conditions by ATP-fueled proteolytic machineries. Among the five AAA+ proteases in Escherichia coli FtsH is the only essential and membrane-anchored metalloprotease. FtsH is a homohexamer that uses its ATPase domain to unfold and translocate substrates that are subsequently degraded without the need of ATP in the proteolytic chamber of the protease domain. FtsH eliminates misfolded proteins in the context of general quality control and properly folded proteins for regulatory reasons. Recent trapping approaches have revealed a number of novel FtsH substrates. This review summarizes the substrate diversity of FtsH and presents details on the surprisingly diverse recognition principles of three well-characterized substrates: LpxC, the key enzyme of lipopolysaccharide biosynthesis; RpoH, the alternative heat-shock sigma factor and YfgM, a bifunctional membrane protein implicated in periplasmic chaperone functions and cytoplasmic stress adaptation.

Bioinspired Bifunctional Membrane for Efficient Clean Water Generation.

Solving the problems of water pollution and water shortage is an urgent need for the sustainable development of modern society. Different approaches, including distillation, filtration, and photocatalytic degradation, have been developed for the purification of contaminated water and the generation of clean water. In this study, we explored a new approach that uses solar light for both water purification and clean water generation. A bifunctional membrane consisting of a top layer of TiO2 nanoparticles (NPs), a middle layer of Au NPs, and a bottom layer of anodized aluminum oxide (AAO) was designed and fabricated through multiple filtration processes. Such a design enables both TiO2 NP-based photocatalytic function and Au NP-based solar-driven plasmonic evaporation. With the integration of these two functions into a single membrane, both the purification of contaminated water through photocatalytic degradation and the generation of clean water through evaporation were demonstrated using simulated solar illumination. Such a demonstration should also help open up a new strategy for maximizing solar energy conversion and utilization.

60 YEARS OF POMC: From POMC and α-MSH to PAM, molecular oxygen, copper, and vitamin C.

A critical role for peptide C-terminal amidation was apparent when the first bioactive peptides were identified. The conversion of POMC into adrenocorticotropic hormone and then into α-melanocyte-stimulating hormone, an amidated peptide, provided a model system for identifying the amidating enzyme. Peptidylglycine α-amidating monooxygenase (PAM), the only enzyme that catalyzes this modification, is essential; mice lacking PAM survive only until mid-gestation. Purification and cloning led to the discovery that the amidation of peptidylglycine substrates proceeds in two steps: peptidylglycine α-hydroxylating monooxygenase catalyzes the copper- and ascorbate-dependent α-hydroxylation of the peptidylglycine substrate; peptidyl-α-hydroxyglycine α-amidating lyase cleaves the N-C bond, producing amidated product and glyoxylate. Both enzymes are contained in the luminal domain of PAM, a type 1 integral membrane protein. The structures of both catalytic cores have been determined, revealing how they interact with metals, molecular oxygen, and substrate to catalyze both reactions. Although not essential for activity, the intrinsically disordered cytosolic domain is essential for PAM trafficking. A phylogenetic survey led to the identification of bifunctional membrane PAM in Chlamydomonas, a unicellular eukaryote. Accumulating evidence points to a role for PAM in copper homeostasis and in retrograde signaling from the lumen of the secretory pathway to the nucleus. The discovery of PAM in cilia, cellular antennae that sense and respond to environmental stimuli, suggests that much remains to be learned about this ancient protein.

Research on Unitized Regenerative Fuel Cell Stack with Producing High Pressure H2 and O2 in WE Mode

A unitized regenerative fuel cell (URFC) is an electrochemical energy storage device that combines a fuel cell and a water electrolyzer in a single system. The URFC is an excellent clean, quite energy source and are promising energy storage systems for uninterrupted power supplies, solar powered aircraft, and satellites. In the paper, the high pressure unitized regenerative fuel cell was developed and validated with a capacity of producing hydrogen and oxygen at a pressure of up to 5MPa in the water electrolysis mode. The bifunctional performance of URFC stack in the hydrogen and oxygen fuel cell (FC) and water electrolysis (WE) modes and the generated gases pressure influence on URFC stack were investigated. The main electrochemical element is bifunctional membrane electrode assembly (MEA) with an active area of 200cm2 which consists of polymer electrolyte membrane from Dupont and the electrode layer on both sides of the membrane by catalyst coated on membrane technique (CCM). Oxygen electrode layer was prepared by Pt/IrO2mixing catalysts. Hydrogen electrode layer was prepared by 40%Pt/C (J.M.). The diffusion layer of MEA was the porous sintered metal foil with corrosion resistance. Primary test results illustrated that high pressure URFC stack exhibited the promising bifunctional performance. The static seal level of URFC stack was up to 10MPa and the dynamic gas pressure reached 5MPa in the water electrolysis mode. Figure1 showed that the stack output electric power was greater than 1.2kW at a current density of 1000mA/cm2in the fuel cell mode. Figure 2 showed that the generated gases pressure had few influence on the performance of the stack in the water electrolysis mode under working conditions. The single cell voltage was 5~12mV higher at the generated gases pressure of up to 5MPa when the current density was less than 700mA/cm2. However the single cell voltage was 5~10mV lower at the generated gases pressure of up to 5MPa when the current density greater than 700mA/cm2. The stack showed good pressure adaptability. The round-trip energy conversion efficiency of high pressure URFC stack was greater than 45% at the current density of 500mA/cm2. In addition, the cycling test of the stack during URFC operation was performed in both fuel cell and water electrolysis modes. The results indicated that high pressure URFC stack had the promising cycling stability. Further research and validation are still underway. Figure 1

Direct Hydroxylation of Benzene to Phenol Using Palladium–Titanium Silicalite Zeolite Bifunctional Membrane Reactors

A series of titanium silicalite zeolite catalysts were successfully incorporated inside a Pd membrane reactor aiming to improve the direct hydroxylation of benzene to phenol. The correlation between the membrane structure and the reaction efficiency was investigated. The influences of reactor configuration, feed mode, and catalysts on benzene conversion, product yield, hydrogen conversion, and water production rate were examined in detail. The reaction was very sensitive to the porosity of Ti-containing zeolite film and the bonding state of the titanium atom in the titanosilicates (i.e., framework and extraframework titanium). The framework titanium could adsorb active oxygen species to form Ti peroxo species which would suppress the decomposition, while the extraframework titanium promoted the decomposition of active oxygen species leading to more water production. Large inter- and intracrystalline pores as well as mesopores provided the reactive species greater opportunity to contact directly with frame...

Innexin and pannexin channels and their signaling

Innexins are bifunctional membrane proteins in invertebrates, forming gap junctions as well as non-junctional membrane channels (innexons). Their vertebrate analogues, the pannexins, have not only lost the ability to form gap junctions but are also prevented from it by glycosylation. Pannexins appear to form only non-junctional membrane channels (pannexons). The membrane channels formed by pannexins and innexins are similar in their biophysical and pharmacological properties. Innexons and pannexons are permeable to ATP, are present in glial cells, and are involved in activation of microglia by calcium waves in glia. Directional movement and accumulation of microglia following nerve injury, which has been studied in the leech which has unusually large glial cells, involves at least 3 signals: ATP is the "go" signal, NO is the "where" signal and arachidonic acid is a "stop" signal.

Improving Stability and Biocompatibility of Alginate/Chitosan Microcapsule by Fabricating Bi‐Functional Membrane

Cell encapsulation technology holds promise for the cell-based therapy. But poor mechanical strength and biocompatibility of microcapsule membrane are still obstacles for the clinical applications. A novel strategy is presented to prepare AC₁ C₂ A microcapsules with bi-functional membrane (that is, both desirable biocompatibility and membrane stability) by sequentially complexing chitosans with higher deacetylation degree (C₁) and lower deacetylation degree (C₂) on alginate (A) gel beads. Both in vitro and in vivo evaluation of AC₁C₂ A microcapsules demonstrate higher membrane stability and less cell adhesion, because the introduction of C₂ increases membrane strength and decreases surface roughness. Moreover, diffusion test of AC₁C₂ A microcapsules displays no inward permeation of IgG protein suggesting good immunoisolation function. The results demonstrate that AC₁C₂ A microcapsules with bi-functional membrane could be a promising candidate for microencapsulated cell implantation with cost effective usage of naturally biocompatible polysaccharides.

Bi-functional hydrogen membrane for simultaneous chemical reaction and hydrogen separation

As a novel approach to simultaneous water–gas shift (WGS) reaction and separation for the production of hydrogen, a bi-functional membrane was successfully prepared using a simple coating method. The catalyst materials, Pt and CeO2, were directly coated over the surface of a Pd–Au dense membrane for excluding slow hydrogen diffusion through the conventional catalyst bed. The coated catalyst layer did not significantly affect the hydrogen permeance of the bare membrane, due to the presence of metal within the catalyst compositions which acted as a bridge for the surface diffusion of hydrogen atoms. As a result of WGS reaction within the novel membrane reactor at 380 °C, the CO conversion was 2 times higher than that of no hydrogen separation. The catalyst-deposited membrane can make the “simultaneous chemical reaction and separation” more feasible and relatively simple, if the more robust catalysts can be loaded with the increased active surface area and the multi-membrane module reactor adopted the coin-shape bi-functional membranes can be designed to completely treat the CO and separate hydrogen from the CO mixture.

Bifunctional palladium composite membrane for hydrogen separation and catalytic CO methanation

NiO was introduced into the porous Al 2 O 3 substrate by impregnation, and the resulting NiO/Al 2 O 3 was coated with the lead of a 2B pencil to modify its surface. A palladium layer with a thickness of 5 μm was deposited by electroless plating on the Pencil/NiO/Al 2 O 3 substrate, and a Pd/Pencil/Ni/Al 2 O 3 membrane was obtained after reduction with hydrogen. For reference, a Ni-free Pd/Pencil/Al 2 O 3 membrane was also fabricated. The surface and cross-sectional morphologies of the membranes were studied by scanning electron microscopy and metallographic microscopy. The hydrogen permeation kinetics was investigated by single gas tests, and the hydrogen separation performances of the Pd/Pencil/Al 2 O 3 and Pd/Pencil/NiO/Al 2 O 3 membranes were tested with a hydrogen feed composed of H 2 77.8%, CO 5.2%, CO 2 13.5%, and CH 4 3.5%. The Ni-free Pd/Pencil/Al 2 O 3 membrane only shows function of hydrogen separation, while the Pd/Pencil/Ni/Al 2 O 3 is also catalytically effective for methanation of CO and CO 2 in hydrogen, forming a bifunctional palladium membrane concept. Since the amount of CO and CO 2 in the hydrogen after membrane separation is very low, the consumption of hydrogen by the methanation reactions is negligible. The bifunctional membrane is promising for proton exchange membrane fuel cells because the catalytic methanation treatment solves the CO poisoning problem of the fuel cell electrodes and consequently allows the palladium membrane to tolerate more membrane defects and to achieve longer life. Aiming at the hydrogen purification for proton exchange membrane fuel cells, a bifunctional Pd/Pencil/Ni/Al 2 O 3 membrane that is capable of hydrogen separation and catalytic CO methanation was developed. It was compared with the Pd/Pencil/Al 2 O 3 membrane without the nickel methanation catalyst.

Effect of cerium dioxide nanoparticles on the expression of selected growth and transcription factors in human astrocytes

AbstractThis study was undertaken to examine the effect of cerium dioxide nanoparticles on the expression levels of genes, encoded transcription and growth factors, which are important for control of cell proliferation and survival in human astrocytes. Exposure of astrocytes with cerium dioxide nanoparticles (0.17 and 0.34 mg/ml of medium) during 20 h significantly decreases the expression level of transcription factors TBX3, E2F8 and FOXF1 mRNAs, being stronger for higher doses of nanoparticles. Moreover, the expression levels of IGFBP1 and IGFBP2 as well as LIF mRNA also significantly decreased in astrocytes after treatment with cerium dioxide nanoparticles. It is possible that the observed changes in the expression profile of the studied genes in astrocytes treated with cerium dioxide nanoparticles are associated with its toxic effect mediated by endoplasmic reticulum stress sensor‐signaling systems in part through the bifunctional membrane enzyme ERN1. Thus, cerium dioxide nanoparticles have a significant effect on important regulatory mechanisms, which control cell proliferation and survival in human astrocytes.

Immuno-contraceptive potential of sperm specific LDHC<sub>4</sub> and SPAM-1 (PH-20) sub units in dog

PH-20 (Spam-1) antigen appears to be a bi-functional sperm plasma membrane protein with hyaluronidase activity and its role is related to cumulus penetration as well as zona binding. (LDH-C4) is a key enzyme, distributed specifically in testis and is highly immunogenic, function of which relates to energy metabolism and capacitation of the sperm. Therefore, in this study, we observed the effect of purified native PH-20 and LDH-C4 antigens on sperm function and morphology in dog. Native PH-20 (46, 32 kDa) and LDH-C4 (36, 30, 28) sub units, purified from dog sperm SDS- extracts were used to test as immunocontraceptive candidates in stray dog. Dogs 1, 2, 3, 4, 5/6 and 7/8 were immunized with 46, 32, 36, 30/28, 46/32, 36/30/28 kDa sub units respectively by i/m route and semen was analysed at weekly intervals. High titre of 3200 - 6400 was achieved in all dogs after three boosters. Immune response in treated dogs was confirmed by increase in Ig level in blood serum and reaction of partially purified serum Ig of immunized dogs with respective antigens in double immune diffusion and immunoblots. Immunization of dogs either with individual PH-20/ LDHC sub units or pooled PH-20/LDHC4 sub units showed a significant effect on sperm count, percent motility, viability, HOST and sperm morphology. All the sperm parameters declined to a significant level (p 4 (36/30/28 kDa) sub units had an immunocontraceptive potential in dog.

Reactive Deposition of Palladium Nanoparticles onto Zeolite Membranes in Supercritical CO2

Pd/Si-MFI membranes are fabricated by depositing palladium nanoparticles onto Si-MFI membranes via opposing reactants chemical fluid deposition in supercritical carbon dioxide. Palladium hexafluoroacetylacetonate [Pd(hfac)2] and ethanol are used as the Pd precursor and the reducing agent, respectively, in the deposition process. The resulting Pd/Si-MFI membrane is characterized using SEM, XRD, EPMA, TEM, and EDX techniques. It is demonstrated that a continuous layer of Pd particles with size of 10 nm is covered on the matrix surface while 30-nm Pd particles are plugged into the defects within the matrix. The H2/N2 permselectivity has been significantly increased due to the deposition of Pd nanoparticles in the Si-MFI membrane, which could keep stable below the critical temperature. This bifunctional membrane and similar membranes possess the application potential to achieve various one-step syntheses.

Palladium-based bifunctional membrane reactor for one-step conversion of benzene to phenol and cyclohexanone

On the one-step hydroxylation of benzene to phenol over a Pd membrane reactor, the bifunctional effects between Pd membrane and metal particles were investigated. In this reaction system, the active oxygen species are formed by the reaction with the permeated hydrogen and adsorbed oxygen over Pd membrane. The active oxygen species are reacted with benzene and directly converts into phenol. For improving this system, various active metals were loaded on the α-Al 2O 3 porous tube which was the substrate of the thin Pd membrane. The loading of noble metals resulted in the enhancement of the activity of side reactions, i.e., complete oxidation and hydrogenation, and a decrease in the hydroxylation activity. The negative effect on hydroxylation was due to the imbalance between the catalytic activities of highly dispersed noble metal particles and the Pd membrane, which has a relatively small surface area. In contrast, the loading of Cu suppressed complete oxidation and enhanced the hydroxylation activity. This effect was mainly due to the increase in the hydrogenation activity without significant acceleration of oxidation. In addition, the potential for the selective conversion of benzene to cyclohexanone by this reactor was discussed.

Gamma-radiation-induced grafting of binary mixture of methacrylic acid and 4-vinyl pyridine onto Teflon-FEP film as an effective polar membrane for separation processes

Ionic bifunctional membranes have been synthesized by grafting binary mixture of methacrylic acid (MAAc) and 4-vinyl pyridine (4-VP) onto Teflon-FEP film by pre-irradiation method. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage of grafting of binary mixture (MAAc-co-4-VP) (71.29%) was obtained at an optimum total dose of 54.48 kGy and the total concentration was 9.49 mol/L ([4-VP] = 0.07 mol/L and [MAAc ] = 9.42 mol/L) in 5 ml of water. The effect of alcohols as additives to the reaction medium on percent grafting of the binary mixture has also been studied. The membranes were characterized by FTIR spectroscopy, scanning electron microscopy and thermogravimetric analysis. Swelling studies of the membranes were performed in different solvents such as water, benzene, carbon tetrachloride and dimethyl formamide (DMF). Maximum swelling was observed in DMF with minimum swelling in benzene. Metal ion (Cu 2+ , Ni 2+ and Fe 2+ ) uptake studies show better affinity for Fe 2+ ions. Conductance measurements in different aqueous salt solution showed that these membranes have affinity for Na + /K + ions and Cl − ions and hence can be used in desalination/separation processes for the separation of both type of cationic and anionic ions.

Studies on the insulinomimetic effects of benzylamine, exogenous substrate of semicarbazide-sensitive amine oxidase enzyme in streptozotocin induced diabetic rats

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO) is believed to be a bifunctional membrane protein. It is localized extracellularly and preferentially oxidizes short chain primary amines to aldehydes, hydrogen peroxide and ammonia, but also functions as an adhesion molecule, which is involved in leukocyte migration. Serum SSAO activity is increased in diabetic patients and animals and the aldehydes formed in the enzyme reaction may contribute to vascular damage. However, administration of exogenous substrates has been shown to improve glucose tolerance and reduce hyperglycaemia in diabetic animals. Hydrogen peroxide and/or its vanadate complexes have been suggested responsible for these effects. Streptozotocin induced diabetic rats were treated with benzylamine (BZA) +/- vanadate (V) or insulin. In contrast to insulin, BZA + V treatment did not reduce HbA(1C) levels. However, it reduced the elevated serum SSAO activity, decreased the accumulation of advanced-glycation end products and increased the bioavailability of nitric oxide in diabetic animals, similarly to insulin. BZA alone did not affect any of these parameters.

Simultaneous purification and immobilization of penicillin G acylase using bifunctional membrane

In this study, the bifunctional membrane (epoxy and immobilized copper ion) was constructed to study the effect on penicillin G acylase (PGA) purification and immobilization. In the procedures, PGA was firstly chelated with the immobilized copper on the membrane at 18 °C, for 12 h. Then, it was covalently bound to the membrane via epoxy group under the incubation conditions (i.e., pH 10.0, 18 °C, 76 h). In the construction of bifunctional membrane, iminodiacetic acid disodium (IDA) concentration critically affected the bifunctional group ratio in the membrane. When IDA concentration was higher than 0.500 M, the chelated copper ion in membrane reached its a saturation of 52.2 μmol/disc. Meanwhile, when IDA concentration was 0.050 M, the chelated copper ion would reach 29.9 μmol/disc, nearly 58% of its saturation. The membrane prepared by 0.05 M IDA was employed to simultaneously purify and immobilize PGA. The resulting PGA membrane was stable even when the chelated copper ion was eluted with ethylenediaminetetraacetic acid disodium salt dehydrate. It was noted that 96.3% of the PGA activity could be retained under 26 times’ reactions within more than 2 months. With this stable property, this immobilization approach could be further developed and applied for industrial processes.

Fabrication of bifunctional membrane electrode assemblies for unitised regenerative polymer electrolyte fuel cells

Bifunctional membrane electrode assemblies have been fabricated using a screen printing technique, which demonstrate a repeatable and stable operation to cell current and voltages. This approach lends itself to a rapid, low-cost and repeatable fabrication process for bifunctional catalytic electrodes in polymer electrolyte membrane fuel cells and electrolysers.

Preparation and characterization of two-layered mordenite-ZSM-5 bi-functional membranes

Two-layered H-ZSM-5-mordenite membranes have been prepared on alumina tubular supports. The objective of this work is to merge the catalytic activity of H-ZSM-5 with the pervaporation water selectivity of mordenite membranes, i.e. to produce true bi-functional zeolite membranes. To be sure that the needed thermal treatment (to remove TPAOH template from the H-ZSM-5 pores) stage did not alter the hydrophilic character of these two-layered H-ZSM-5-mordenite membranes, the calcination was carried out under a steam/air atmosphere. Experiments concerning the pervaporation of water/ethanol mixtures and the esterification of acetic acid with ethanol were performed to demonstrate the applicability of the membranes prepared here.

A single aquaporin gene encodes a water/glycerol/urea facilitator in Toxoplasma gondii with similarity to plant tonoplast intrinsic proteins

We describe a single aquaporin gene in Toxoplasma gondii which, surprisingly, has only 28% sequence similarity to the aquaglyceroporin of another apicomplexan parasite, Plasmodium falciparum. Sequence comparisons showed 47% similarity to water-specific plant aquaporins and the conservation of typical pore-forming residues. We established that the Toxoplasma aquaporin protein is a bifunctional membrane pore with intermediate water and high glycerol permeability. Furthermore, we identified hydroxyurea, an antineoplastic agent with inhibitory effects on parasite proliferation, as a permeant of this channel.

Kinetic resolution of chiral alcohols in bifunctional membrane exhibiting enzyme activity and enantioselective permeation

The paper deals with the kinetic resolution of chiral alcohols in a transesterification process performed in the reactor containing a bifunctional polymer membrane. The membrane was prepared using an asymmetric polyamide film. It exhibits enantioselective permeabilities caused by an embedded imprinted polymer as well as catalytic properties induced by the immobilised lipase. The transesterification of vinyl acetate with (±)- trans-2-phenyl-1-cyclohexanol, performed in the reactor with the bifunctional membrane, gives chiral products of high purity. In this case, the enantiomeric excess (e.e.) of the product exceeds 98% while it reaches 80% only when the reactor with a common enzyme membrane is used.