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Gerhard Hummer - One of the best experts on this subject based on the ideXlab platform.
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regulation of lipid saturation without sensing Membrane fluidity
Nature Communications, 2020Co-Authors: Stephanie Ballweg, Erdinc Sezgin, Milka Doktorova, Roberto Covino, John Reinhard, Dorith Wunnicke, Inga Hanelt, Ilya Levental, Gerhard HummerAbstract:Cells maintain Membrane fluidity by regulating lipid saturation, but the molecular mechanisms of this homeoviscous adaptation remain poorly understood. We have reconstituted the core machinery for regulating lipid saturation in baker’s yeast to study its molecular mechanism. By combining molecular dynamics simulations with experiments, we uncover a remarkable sensitivity of the transcriptional regulator Mga2 to the abundance, position, and configuration of double bonds in lipid acyl chains, and provide insights into the molecular rules of Membrane adaptation. Our data challenge the prevailing hypothesis that Membrane fluidity serves as the measured variable for regulating lipid saturation. Rather, we show that Mga2 senses the molecular lipid-packing density in a defined region of the Membrane. Our findings suggest that Membrane Property sensors have evolved remarkable sensitivities to highly specific aspects of Membrane structure and dynamics, thus paving the way toward the development of genetically encoded reporters for such properties in the future. Cells maintain Membrane fluidity by regulating lipid saturation, but the molecular mechanisms of this homeoviscous adaptation remain poorly understood. Here authors reconstituted the core machinery for regulating lipid saturation in baker’s yeast to directly characterize its response to defined Membrane environments and uncover its mode-of-action.
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regulation of lipid saturation without sensing Membrane fluidity
Nature Communications, 2020Co-Authors: Stephanie Ballweg, Erdinc Sezgin, Milka Doktorova, Roberto Covino, John Reinhard, Dorith Wunnicke, Inga Hanelt, Ilya Levental, Gerhard HummerAbstract:Cells maintain Membrane fluidity by regulating lipid saturation, but the molecular mechanisms of this homeoviscous adaptation remain poorly understood. We have reconstituted the core machinery for regulating lipid saturation in baker's yeast to study its molecular mechanism. By combining molecular dynamics simulations with experiments, we uncover a remarkable sensitivity of the transcriptional regulator Mga2 to the abundance, position, and configuration of double bonds in lipid acyl chains, and provide insights into the molecular rules of Membrane adaptation. Our data challenge the prevailing hypothesis that Membrane fluidity serves as the measured variable for regulating lipid saturation. Rather, we show that Mga2 senses the molecular lipid-packing density in a defined region of the Membrane. Our findings suggest that Membrane Property sensors have evolved remarkable sensitivities to highly specific aspects of Membrane structure and dynamics, thus paving the way toward the development of genetically encoded reporters for such properties in the future.
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integrated functions of Membrane Property sensors and a hidden side of the unfolded protein response
Molecular Cell, 2018Co-Authors: Roberto Covino, Gerhard Hummer, Robert K ErnstAbstract:Eukaryotic cells face the challenge of maintaining the complex composition of several coexisting organelles. The molecular mechanisms underlying the homeostasis of subcellular Membranes and their adaptation during stress are only now starting to emerge. Here, we discuss three Membrane Property sensors of the endoplasmic reticulum (ER), namely OPI1, MGA2, and IRE1, each controlling a large cellular program impacting the lipid metabolic network. OPI1 coordinates the production of Membrane and storage lipids, MGA2 regulates the production of unsaturated fatty acids required for Membrane biogenesis, and IRE1 controls the unfolded protein response (UPR) to adjust ER size, protein folding, and the secretory capacity of the cell. Although these proteins use remarkably distinct sensing mechanisms, they are functionally connected via the ER Membrane and cooperate to maintain Membrane homeostasis. As a rationalization of the recently described mechanism of UPR activation by lipid bilayer stress, we propose that IRE1 can sense the protein-to-lipid ratio in the ER Membrane to ensure a balanced production of Membrane proteins and lipids.
Paraiso, Lara Ferreira - One of the best experts on this subject based on the ideXlab platform.
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Efeito do exercício físico na estabilidade de membrana de eritrócitos
Universidade Federal de Uberlândia, 2015Co-Authors: Paraiso, Lara FerreiraAbstract:CAPÍTULO II - Este estudo avaliou os efeitos de dois tipos diferentes de exercício aeróbio sobre a estabilidade osmótica da membrana do eritrócito humano e em diferentes variáveis hematológicas e bioquímicas que estão associados a esta propriedade da membrana. A população do estudo consistiu de 20 homens saudáveis e ativos. Os participantes realizaram sessões únicas de dois tipos de exercício. A primeira sessão foi constituída por 60 min de exercício contínuo de intensidade moderada (MICE). A segunda sessão, executada uma semana depois, consistiu em uma sessão de exercício intervalado de alta intensidade (HIIE) até a exaustão. A estabilidade osmótica da membrana dos eritrócitos foi representada pelo inverso da concentração de sal (1/H50) no ponto médio da curva sigmoidal de dependência entre a absorbância da hemoglobina e a concentração de NaCl. Os valores de 1/H50 se alteraram de 2,29±0,1 para 2,33±0,09 após MICE e de 2,30± 0,08 para 2,23±0,12 após HIIE. Durante o MICE o volume corpuscular médio aumentou, provavelmente devido à lise in vivo dos eritrócitos mais velhos, com preservação de células que eram maiores e mais resistentes a lise in vitro. O estudo mostrou que uma única sessão de exercício agudo afetou a estabilidade osmótica de eritrócitos, ocorrendo aumento após MICE e diminuição após HIIE. CAPÍTULO III - Objetivo Este estudo teve por objetivo avaliar a influência de exercício agudo e crônico sobre a estabilidade de membrana de eritrócitos e vários índices sanguíneos em uma população constituída por 5 atletas do sexo masculino de nível nacional na modalidade natação, ao longo de 18 semanas de treinamento. Método As avaliações foram feitas ao início e final da 1ª, 7ª, 13ª e 18ª semanas, quando foram feitas alterações no volume e intensidade de treinamento. Os efeitos manifestados no início daquelas semanas foram considerados decorrentes de adaptações crônicas, enquanto os efeitos observados ao final das semanas foram considerados decorrentes de manifestações agudas da carga de exercício daquela semana. Resultados As alterações agudas decorrentes do exercício compreenderam aumento na atividade da creatina quinase (CK) e na quantidade de leucócitos (Leu), e diminuição no hematócrito (Ht) e volume corpuscular médio (MCV), ao final da primeira semana; aumento nas atividades da CK e da lactato desidrogenase (LDH) e nas concentrações de ácido úrico (UA) e Leu, ao final da sétima semana; aumento nos valores de CK, LDH e concentração de hemoglobina corpuscular média (MCHC), ao final da 13ª semana; e diminuição dos valores do índice de estabilidade osmótica de eritrócitos 1/H50 e aumento na atividade da CK e na concentração de plaquetas (Plt), ao final da 18ª semana. As alterações crônicas decorrentes do treinamento compreenderam aumento dos valores de 1/H50, CK, LDH, colesterol da lipoproteína de alta densidade (HDL-C), colesterol da lipoproteína de baixa densidade (LDL-C), ferro sérico (Fe), MCV e Plt. Conclusão Apesar de o treinamento agudo ter resultado em diminuição na estabilidade osmótica de eritrócitos, provavelmente associada à exacerbação de processos oxidativos durante o exercício intenso, o treinamento crônico ao longo das 18 semanas, resultou em aumento na estabilidade osmótica de eritrócitos, provavelmente pela modulação do teor de colesterol de membrana pelas lipoproteínas de baixa e alta densidade.CHAPTER II - This study evaluated the effects of two different types of acute aerobic exercise on the osmotic stability of human erythrocyte Membrane and on different hematological and biochemical variables that are associated with this Membrane Property. The study population consisted of 20 healthy and active men. Participants performed single sessions of two types of exercise. The first session consisted of 60 min of moderate-intensity continuous exercise (MICE). The second session, executed a week later, consisted of high-intensity interval exercise (HIIE) until exhaustion. The osmotic stability of the erythrocyte Membrane was represented by the inverse of the salt concentration (1/H50) at the midpoint of the sigmoidal curve of dependence between the absorbance of hemoglobin and the NaCl concentration. The values of 1/H50 changed from 2.29 ± 0.1 to 2.33 ± 0.09 after MICE and from 2.30 ± 0.08 to 2.23 ± 0.12 after HIIE. In MICE has occurred an increase in the mean corpuscular volume, probably due to in vivo lysis of older erythrocytes, with preservation of cells that were larger and more resistant to in vitro lysis. The study showed that a single bout of acute exercise affected the erythrocyte osmotic stability, which increased after MICE and decreased after HIIE.CHAPTER III - Objective This study aimed to evaluate the influence of acute and chronic exercise on erythrocyte Membrane stability and various blood indices in a population consisting of five national-level male swimmers, over 18 weeks of training. Method The evaluations were made at the beginning and end of the 1st, 7th, 13th and 18th weeks, when volume and training intensity have changed. The effects manifested at the beginning of those weeks were considered due to chronic adaptations, while the effects observed at the end of the weeks were considered due to acute manifestations of the exercise load of that week. Results Acute changes resulting from the exercise comprised increases in creatine kinase activity (CK) and leukocyte count (Leu), and decrease in hematocrit (Ht) and mean corpuscular volume (MCV), at the end of the first week; increase in the activities of CK and lactate dehydrogenase (LDH), in the uric acid (UA) concentration and Leu count, at the end of the seventh week; increases in CK and LDH activities and in the mean corpuscular hemoglobin concentration (MCHC), at the end of the 13th week; and decrease in the value of the osmotic stability index 1/H50 and increases in the CK activity and platelets (Plt) count, at the end of the 18th week. Chronic changes due to training comprised increase in the values of 1/H50, CK, LDH, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), serum iron (Fe), MCV and Plt. Conclusion Although acute training have resulted in decrease in the osmotic stability of erythrocytes, probably associated with exacerbation of the oxidative processes during intense exercise, chronic training over 18 weeks resulted in increased osmotic stability of erythrocytes, probably by modulation in the Membrane cholesterol content by low and high density lipoproteins
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Efeito do exercício físico na estabilidade de membrana de eritrócitos
'EDUFU - Editora da Universidade Federal de Uberlandia', 2015Co-Authors: Paraiso, Lara FerreiraAbstract:CHAPTER II - This study evaluated the effects of two different types of acute aerobic exercise on the osmotic stability of human erythrocyte Membrane and on different hematological and biochemical variables that are associated with this Membrane Property. The study population consisted of 20 healthy and active men. Participants performed single sessions of two types of exercise. The first session consisted of 60 min of moderate-intensity continuous exercise (MICE). The second session, executed a week later, consisted of high-intensity interval exercise (HIIE) until exhaustion. The osmotic stability of the erythrocyte Membrane was represented by the inverse of the salt concentration (1/H50) at the midpoint of the sigmoidal curve of dependence between the absorbance of hemoglobin and the NaCl concentration. The values of 1/H50 changed from 2.29 ± 0.1 to 2.33 ± 0.09 after MICE and from 2.30 ± 0.08 to 2.23 ± 0.12 after HIIE. In MICE has occurred an increase in the mean corpuscular volume, probably due to in vivo lysis of older erythrocytes, with preservation of cells that were larger and more resistant to in vitro lysis. The study showed that a single bout of acute exercise affected the erythrocyte osmotic stability, which increased after MICE and decreased after HIIE.CHAPTER III - Objective This study aimed to evaluate the influence of acute and chronic exercise on erythrocyte Membrane stability and various blood indices in a population consisting of five national-level male swimmers, over 18 weeks of training. Method The evaluations were made at the beginning and end of the 1st, 7th, 13th and 18th weeks, when volume and training intensity have changed. The effects manifested at the beginning of those weeks were considered due to chronic adaptations, while the effects observed at the end of the weeks were considered due to acute manifestations of the exercise load of that week. Results Acute changes resulting from the exercise comprised increases in creatine kinase activity (CK) and leukocyte count (Leu), and decrease in hematocrit (Ht) and mean corpuscular volume (MCV), at the end of the first week; increase in the activities of CK and lactate dehydrogenase (LDH), in the uric acid (UA) concentration and Leu count, at the end of the seventh week; increases in CK and LDH activities and in the mean corpuscular hemoglobin concentration (MCHC), at the end of the 13th week; and decrease in the value of the osmotic stability index 1/H50 and increases in the CK activity and platelets (Plt) count, at the end of the 18th week. Chronic changes due to training comprised increase in the values of 1/H50, CK, LDH, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), serum iron (Fe), MCV and Plt. Conclusion Although acute training have resulted in decrease in the osmotic stability of erythrocytes, probably associated with exacerbation of the oxidative processes during intense exercise, chronic training over 18 weeks resulted in increased osmotic stability of erythrocytes, probably by modulation in the Membrane cholesterol content by low and high density lipoproteins.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorTese (Doutorado)CAPÍTULO II - Este estudo avaliou os efeitos de dois tipos diferentes de exercício aeróbio sobre a estabilidade osmótica da membrana do eritrócito humano e em diferentes variáveis hematológicas e bioquímicas que estão associados a esta propriedade da membrana. A população do estudo consistiu de 20 homens saudáveis e ativos. Os participantes realizaram sessões únicas de dois tipos de exercício. A primeira sessão foi constituída por 60 min de exercício contínuo de intensidade moderada (MICE). A segunda sessão, executada uma semana depois, consistiu em uma sessão de exercício intervalado de alta intensidade (HIIE) até a exaustão. A estabilidade osmótica da membrana dos eritrócitos foi representada pelo inverso da concentração de sal (1/H50) no ponto médio da curva sigmoidal de dependência entre a absorbância da hemoglobina e a concentração de NaCl. Os valores de 1/H50 se alteraram de 2,29±0,1 para 2,33±0,09 após MICE e de 2,30± 0,08 para 2,23±0,12 após HIIE. Durante o MICE o volume corpuscular médio aumentou, provavelmente devido à lise in vivo dos eritrócitos mais velhos, com preservação de células que eram maiores e mais resistentes a lise in vitro. O estudo mostrou que uma única sessão de exercício agudo afetou a estabilidade osmótica de eritrócitos, ocorrendo aumento após MICE e diminuição após HIIE. CAPÍTULO III - Objetivo Este estudo teve por objetivo avaliar a influência de exercício agudo e crônico sobre a estabilidade de membrana de eritrócitos e vários índices sanguíneos em uma população constituída por 5 atletas do sexo masculino de nível nacional na modalidade natação, ao longo de 18 semanas de treinamento. Método As avaliações foram feitas ao início e final da 1ª, 7ª, 13ª e 18ª semanas, quando foram feitas alterações no volume e intensidade de treinamento. Os efeitos manifestados no início daquelas semanas foram considerados decorrentes de adaptações crônicas, enquanto os efeitos observados ao final das semanas foram considerados decorrentes de manifestações agudas da carga de exercício daquela semana. Resultados As alterações agudas decorrentes do exercício compreenderam aumento na atividade da creatina quinase (CK) e na quantidade de leucócitos (Leu), e diminuição no hematócrito (Ht) e volume corpuscular médio (MCV), ao final da primeira semana; aumento nas atividades da CK e da lactato desidrogenase (LDH) e nas concentrações de ácido úrico (UA) e Leu, ao final da sétima semana; aumento nos valores de CK, LDH e concentração de hemoglobina corpuscular média (MCHC), ao final da 13ª semana; e diminuição dos valores do índice de estabilidade osmótica de eritrócitos 1/H50 e aumento na atividade da CK e na concentração de plaquetas (Plt), ao final da 18ª semana. As alterações crônicas decorrentes do treinamento compreenderam aumento dos valores de 1/H50, CK, LDH, colesterol da lipoproteína de alta densidade (HDL-C), colesterol da lipoproteína de baixa densidade (LDL-C), ferro sérico (Fe), MCV e Plt. Conclusão Apesar de o treinamento agudo ter resultado em diminuição na estabilidade osmótica de eritrócitos, provavelmente associada à exacerbação de processos oxidativos durante o exercício intenso, o treinamento crônico ao longo das 18 semanas, resultou em aumento na estabilidade osmótica de eritrócitos, provavelmente pela modulação do teor de colesterol de membrana pelas lipoproteínas de baixa e alta densidade
Orlando Coronell - One of the best experts on this subject based on the ideXlab platform.
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effect of feed water ph on the partitioning of alkali metal salts from aqueous phase into the polyamide active layers of reverse osmosis Membranes
Environmental Science & Technology, 2021Co-Authors: Jingbo Wang, Mikayla D Armstrong, Kasia Grzebyk, Riley Vickers, Orlando CoronellAbstract:The partitioning of solutes into the polyamide active layers of reverse osmosis (RO) Membranes is a key Membrane Property determining solute permeation. Quantification of partition coefficients and...
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effect of feed water ph on the partitioning of alkali metal salts from aqueous phase into the polyamide active layers of reverse osmosis Membranes
Environmental Science & Technology, 2021Co-Authors: Jingbo Wang, Mikayla D Armstrong, Kasia Grzebyk, Riley Vickers, Orlando CoronellAbstract:The partitioning of solutes into the polyamide active layers of reverse osmosis (RO) Membranes is a key Membrane Property determining solute permeation. Quantification of partition coefficients and their dependence on feedwater pH would contribute to the development of predictive transport models of contaminant transport through RO Membranes; however, neither solute partitioning nor the effect of feed solution pH on partitioning has been thoroughly characterized in the literature. Accordingly, we characterized the partitioning of all chloride salts of alkali metals (CsCl, RbCl, KCl, NaCl, and LiCl) from the aqueous phase into the polyamide active layers of five polyamide RO Membranes, including one prepared in-house and four commercial Membranes. We evaluated the effect of pH on the partitioning of alkali metal salts and whether the effect of pH on salt partitioning and rejection is consistent with Donnan theory predictions. Results showed that for all Membranes, the partition coefficients of all salts were less than one and did not differ substantially among RO Membranes. Results also indicated that for all Membranes tested, Donnan theory provided an appropriate theoretical framework to estimate the effect of pH on salt partitioning (evaluated for all chloride salts of alkali metals) and salt rejection (evaluated for NaCl). Thus, we conclude that changes in salt rejection resulting from feed solution pH are primarily driven by changes in salt partitioning with comparatively small changes in salt diffusion coefficients.
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Junction Potentials Bias Measurements of Ion Exchange Membrane Permselectivity
Environmental science & technology, 2018Co-Authors: Ryan S. Kingsbury, Sophie Flotron, Shan Zhu, Douglas F. Call, Orlando CoronellAbstract:Ion exchange Membranes (IEMs) are versatile materials relevant to a variety of water and waste treatment, energy production, and industrial separation processes. The defining characteristic of IEMs is their ability to selectively allow positive or negative ions to permeate, which is referred to as permselectivity. Measured values of permselectivity that equal unity (corresponding to a perfectly selective Membrane) or exceed unity (theoretically impossible) have been reported for cation exchange Membranes (CEMs). Such nonphysical results call into question our ability to correctly measure this crucial Membrane Property. Because weighing errors, temperature, and measurement uncertainty have been shown to not explain these anomalous permselectivity results, we hypothesized that a possible explanation are junction potentials that occur at the tips of reference electrodes. In this work, we tested this hypothesis by comparing permselectivity values obtained from bare Ag/AgCl wire electrodes (which have no junct...
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junction potentials bias measurements of ion exchange Membrane permselectivity
ChemRxiv, 2017Co-Authors: Ryan S. Kingsbury, Sophie Flotron, Shan Zhu, Douglas F. Call, Orlando CoronellAbstract:Ion exchange Membranes (IEMs) are versatile materials relevant to a variety of water and waste treatment, energy production, and industrial separation processes. The defining characteristic of IEMs is their ability to selectively allow positive or negative ions to permeate, which is referred to as the permselectivity. Measured values of permselectivity that equal unity (corresponding to a perfectly-selective Membrane) or exceed unity (theoretically impossible) have been reported for cation exchange Membranes (CEMs). Such non-physical results call into question our ability to correctly measure this crucial Membrane Property. Since weighing errors, temperature, and measurement uncertainty have been shown to not explain these anomalous permselectivity results, we hypothesized that a possible explanation are junction potentials that occur at the tips of reference electrodes. In this work, we tested this hypothesis by comparing permselectivity values obtained from bare Ag/AgCl wire electrodes (which have no junction) to values obtained from single-junction reference electrodes containing two different electrolytes. We show that permselectivity values obtained using reference electrodes with junctions were greater than unity for CEMs. By contrast, electrodes without junctions always produced permselectivities lower than unity. Electrodes with junctions also resulted in artificially low permselectivity values for AEMs compared to electrodes without junctions. Thus, we conclude that junctions in reference electrodes introduce two biases into results in the IEM literature: (i) permselectivity values larger than unity for CEMs, and (ii) lower permselectivity values for AEMs compared to those for CEMs. These biases can be avoided by using electrodes without a junction.
Hiroshi Umakoshi - One of the best experts on this subject based on the ideXlab platform.
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quantitative monitoring of microphase separation behaviors in cationic liposomes using hhc dph and laurdan estimation of the local electrostatic potentials in microdomains
Langmuir, 2016Co-Authors: Keishi Suga, Kei Akizaki, Hiroshi UmakoshiAbstract:Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N′,N′-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical Membrane Property analyses, focusing on Membrane fluidity and Membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For...
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quantitative monitoring of microphase separation behaviors in cationic liposomes using hhc dph and laurdan estimation of the local electrostatic potentials in microdomains
Langmuir, 2016Co-Authors: Keishi Suga, Kei Akizaki, Hiroshi UmakoshiAbstract:Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N',N'-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical Membrane Property analyses, focusing on Membrane fluidity and Membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For DOPC/DOTAP = (7/3), the Membrane was in the liquid-disordered phase and the density of cationic molecules was 0.41 cation/nm(2). For DOPC/DC-Ch = (7/3), the Membrane was heterogeneous and the densities of cationic molecules in liquid-disordered and liquid-ordered phases were 0.25 and 1.24 cation/nm(2), respectively. We thereby conclude that the DC-Ch molecules can form nanodomains when these molecules are concentrated to 59%.
Keishi Suga - One of the best experts on this subject based on the ideXlab platform.
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quantitative monitoring of microphase separation behaviors in cationic liposomes using hhc dph and laurdan estimation of the local electrostatic potentials in microdomains
Langmuir, 2016Co-Authors: Keishi Suga, Kei Akizaki, Hiroshi UmakoshiAbstract:Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N′,N′-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical Membrane Property analyses, focusing on Membrane fluidity and Membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For...
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quantitative monitoring of microphase separation behaviors in cationic liposomes using hhc dph and laurdan estimation of the local electrostatic potentials in microdomains
Langmuir, 2016Co-Authors: Keishi Suga, Kei Akizaki, Hiroshi UmakoshiAbstract:Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3β-[N(N',N'-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical Membrane Property analyses, focusing on Membrane fluidity and Membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For DOPC/DOTAP = (7/3), the Membrane was in the liquid-disordered phase and the density of cationic molecules was 0.41 cation/nm(2). For DOPC/DC-Ch = (7/3), the Membrane was heterogeneous and the densities of cationic molecules in liquid-disordered and liquid-ordered phases were 0.25 and 1.24 cation/nm(2), respectively. We thereby conclude that the DC-Ch molecules can form nanodomains when these molecules are concentrated to 59%.