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Abstract
Cell penetrating peptides (CPPs) are natural agents that efficiently permeate biological membranes. They are frequently positively charged, which is surprising since membranes pose hydrophobic barriers. In this Perspective, I discuss computations and experiments of a permeation model that couples permeant displacement with a membrane defect. We call the proposed mechanism Defect Assisted by Charge (DAC) and illustrate that it reduces the free energy barrier for translocation. A metastable state at the center of the membrane may be observed due to the charge interactions with the phospholipid head groups at the two leaflets. The combination of experiments and simulations sheds light on the mechanisms of a charged peptide translocation across phospholipid membranes.
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Affiliation(s)
- Ron Elber
- The Department of Chemistry, The Oden Institute, The University of Texas at Austin, Austin, Texas 78712, United States
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2
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Collins KD. Why continuum electrostatics theories cannot explain biological structure, polyelectrolytes or ionic strength effects in ion–protein interactions. Biophys Chem 2012; 167:43-59. [DOI: 10.1016/j.bpc.2012.04.002] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Revised: 04/10/2012] [Accepted: 04/10/2012] [Indexed: 01/13/2023]
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3
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Shimanouchi T, Walde P, Gardiner J, Mahajan YR, Seebach D, Thomae A, Krämer SD, Voser M, Kuboi R. Permeation of a beta-heptapeptide derivative across phospholipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:2726-36. [PMID: 17714685 DOI: 10.1016/j.bbamem.2007.07.011] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Revised: 06/28/2007] [Accepted: 07/05/2007] [Indexed: 11/30/2022]
Abstract
Based on a number of experiments it is concluded that the fluorescein labeled beta-heptapeptide fluoresceinyl-NH-CS-(S)-beta(3)hAla-(S)-beta(3)hArg-(R)-beta(3)hLeu-(S)-beta(3)hPhe-(S)-beta(3)hAla-(S)-beta(3)hAla-(S)-beta(3)hLys-OH translocates across lipid vesicle bilayers formed from DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine). The conclusion is based on the following observations: (i) addition of the peptide to the vicinity of micrometer-sized giant vesicles leads to an accumulation of the peptide inside the vesicles; (ii) if the peptide is injected inside individual giant vesicles, it is released from the vesicles in a time dependent manner; (iii) if the peptide is encapsulated within sub-micrometer-sized large unilamellar vesicles, it is released from the vesicles as a function of time; (iv) if the peptide is submitted to immobilized liposome chromatography, the peptide is retained by the immobilized DOPC vesicles. Furthermore, the addition of the peptide to calcein-containing DOPC vesicles does not lead to significant calcein leakage and vesicle fusion is not observed. The finding that derivatives of the beta-heptapeptide (S)-beta(3)hAla-(S)-beta(3)hArg-(R)-beta(3)hLeu-(S)-beta(3)hPhe-(S)-beta(3)hAla-(S)-beta(3)hAla-(S)-beta(3)hLys-OH can translocate across phospholipid bilayers is supported by independent measurements using Tb(3+)-containing large unilamellar vesicles prepared from egg phosphatidylcholine and wheat germ phosphatidylinositol (molar ratio of 9:1) and a corresponding peptide that is labeled with dipicolinic acid instead of fluorescein. The experiments show that this dipicolinic acid labeled beta-heptapeptide derivative also permeates across phospholipid bilayers. The possible mechanism of the translocation of the particular beta-heptapeptide derivatives across the membrane of phospholipid vesicles is discussed within the frame of the current understanding of the permeation of certain oligopeptides across simple phospholipid bilayers.
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Affiliation(s)
- Toshinori Shimanouchi
- Department of Chemical Science and Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
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Gardiner J, Thomae AV, Mathad RI, Seebach D, Krämer SD. Comparison of permeation through phosphatidylcholine bilayers of N-dipicolinyl-alpha- and -beta-oligopeptides. Chem Biodivers 2007; 3:1181-201. [PMID: 17193232 DOI: 10.1002/cbdv.200690120] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Cell-membrane permeation of small therapeutic peptides and peptidomimetics is a fundamental issue in pharmaceutical research. Using a Tb(3+)-based permeation assay, we have examined the ability of alpha- and beta-peptides, bearing proteinogenic side chains and an N-terminal dipicolinic acid (DPA) monoamide group, to enter liposomes composed of egg phosphatidylcholine bilayers. A series of 12 DPA-peptides of increasing chain length was prepared and characterized by CD and NMR analysis. An interesting destabilizing effect of the N-terminal DPA group on the helical structure of a beta-hexapeptide was discovered. Significant differences in permeation were observed between the DPA-alpha- and the DPA-beta-peptides, with all beta-peptidic compounds permeating better than their alpha-analogs. Thus, beta-peptides have been shown to interact with lipid bilayers in a manner that is distinctly different from that of alpha-peptides. Together with the fact that beta-peptides are proteolytically stable in mammalian organisms, and that they fold to form helices and hairpin turns with short chain lengths, the new results further emphasize the biomedical potential of beta-peptides.
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Affiliation(s)
- James Gardiner
- Laboratorium für Organische Chemie, Departement Chemie und Angewandte Biowissenschaften, ETH-Zürich, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich
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Soni V, Yasui T, Cahir-McFarland E, Kieff E. LMP1 transmembrane domain 1 and 2 (TM1-2) FWLY mediates intermolecular interactions with TM3-6 to activate NF-kappaB. J Virol 2006; 80:10787-93. [PMID: 16928765 PMCID: PMC1641781 DOI: 10.1128/jvi.01214-06] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The Epstein-Barr virus oncoprotein LMP1 has six transmembrane domains (TMs) that enable intermolecular aggregation and constitutive signaling through two C-terminal cytosolic domains. Expression of both TMs 1 and 2 without the C terminus (TM1-2DeltaC) and TMs 3 to 6 fused to the C terminus (TM3-6) results in partial association, which is substantially decreased by TM1 F38WLY41 mutation to A38ALA41. We now investigate whether TM1-2DeltaC can functionally interact with TM3-6. TM1-2DeltaC induced TM3-6 to mediate NF-kappaB activation at 59% of LMP1 levels, and the effect was dependent on TM1-2 F38WLY41. TM1-2DeltaC even induced TM3-4 C terminus-mediated NF-kappaB activation to 44% of LMP1 levels. Surprisingly, this effect was TM1 F38WLY41 independent, indicative of a role for TMs 5 and 6 in TM1 F38WLY41 effects. TM3 W98 was also important for TM1-2DeltaC induction of TM3-6-mediated NF-kappaB activation, for association, and for TM1 F38WLY41 dependence on C-terminal NF-kappaB activation. These data support models in which the TM1 F38WLY41 effects are at least partially dependent on TM3 W98 and a residue(s) in TMs 5 and 6.
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Affiliation(s)
- Vishal Soni
- Channing Laboratory and Infectious Disease Division, Brigham and Women's Hospital, Boston, MA 02130, USA
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Walde P. Surfactant assemblies and their various possible roles for the origin(s) of life. ORIGINS LIFE EVOL B 2006; 36:109-50. [PMID: 16642266 DOI: 10.1007/s11084-005-9004-3] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Accepted: 11/01/2005] [Indexed: 12/21/2022]
Abstract
A large number of surfactants (surface active molecules) are chemically simple compounds that can be obtained by simple chemical reactions, in some cases even under presumably prebiotic conditions. Surfactant assemblies are self-organized polymolecular aggregates of surfactants, in the simplest case micelles, vesicles, hexagonal and cubic phases. It may be that these different types of surfactant assemblies have played various, so-far underestimated important roles in the processes that led to the formation of the first living systems. Although nucleic acids are key players in the formation of cells as we know them today (RNA world hypothesis), it is still unclear how RNA could have been formed under prebiotic conditions. Surfactants with their self-organizing properties may have assisted, controlled and compartimentalized some of the chemical reactions that eventually led to the formation of molecules like RNA. Therefore, surfactants were possibly very important in prebiotic times in the sense that they may have been involved in different physical and chemical processes that finally led to a transformation of non-living matter to the first cellular form(s) of life. This hypothesis is based on four main experimental observations: (i) Surfactant aggregation can lead to cell-like compartimentation (vesicles). (ii) Surfactant assemblies can provide local reaction conditions that are very different from the bulk medium, which may lead to a dramatic change in the rate of chemical reactions and to a change in reaction product distributions. (iii) The surface properties of surfactant assemblies that may be liquid- or solid-like, charged or neutral, and the elasticity and packing density of surfactant assemblies depend on the chemical structure of the surfactants, on the presence of other molecules, and on the overall environmental conditions (e. g. temperature). This wide range of surface characteristics of surfactant assemblies may allow a control of surface-bound chemical reactions not only by the charge or hydrophobicity of the surface but also by its "softness". (iv) Chiral polymolecular assemblies (helices) may form from chiral surfactants. There are many examples that illustrate the different roles and potential roles of surfactant assemblies in different research areas outside of the field of the origin(s) of life, most importantly in investigations of contemporary living systems, in nanotechnology applications, and in the development of drug delivery systems. Concepts and ideas behind many of these applications may have relevance also in connection to the different unsolved problems in understanding the origin(s) of life.
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Affiliation(s)
- Peter Walde
- ETH Zürich, Department of Materials, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland.
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Yasui T, Luftig M, Soni V, Kieff E. Latent infection membrane protein transmembrane FWLY is critical for intermolecular interaction, raft localization, and signaling. Proc Natl Acad Sci U S A 2003; 101:278-83. [PMID: 14695890 PMCID: PMC314176 DOI: 10.1073/pnas.2237224100] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Relatively little is known about the biochemical mechanisms through which the Epstein-Barr virus latent infection integral membrane protein 1 (LMP1) transmembrane domains cause constitutive LMP1 aggregation and continuous cytoplasmic C terminus-mediated signal transduction. We now evaluate the role of the three consecutive LMP1 hydrophobic transmembrane pairs, transmembrane domains (TM)1-2, TM3-4, and TM5-6, in intermolecular aggregation and NF-kappaB activation. LMP1TM1-2 enabled approximately 40% of wild-type LMP1 cytoplasmic domain-mediated NF-kappaB activation, whereas TM3-4 or TM5-6 assayed in parallel had almost no effect independent of LMP1TM1-2. Alanine mutagenesis of conserved residues in LMP1TM1-2 identified FWLY(38-41) to be critical for LMP1TM1-2 intermolecular association with LMP1TM3-6. Further, in contrast to wild-type LMP1, LMP1 with FWLY(38-41) mutated to AALA(38-41) did not (i). significantly partition to lipid Rafts or Barges and effectively intermolecularly associate, (ii). enable cytoplasmic C terminus engagement of tumor necrosis factor receptor-associated factor 3, (iii). activate NF-kappaB, and thereby (iv). induce tumor necrosis factor receptor-associated factor 1 expression. Other LMP1 intermolecular associations were observed that involved LMP1TM1-2/LMP1TM1-2 or LMP1TM3-4/LMP1TM3-6 interactions; these probably also contribute to LMP1 aggregation. Because FWLY(38-41) was essential for LMP1-mediated signal transduction, and LMP1 activation of NF-kappaB is essential for proliferating B lymphocyte survival, inhibition of LMP1FWLY(41)-mediated LMP1/LMP1 intermolecular interactions is an attractive therapeutic target.
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Affiliation(s)
- Teruhito Yasui
- Brigham and Women's Hospital, Department of Medicine, Harvard University, 181 Longwood Avenue, Boston, MA 02215, USA
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Shang X, Liu Y, Yan E, Eisenthal KB. Effects of Counterions on Molecular Transport Across Liposome Bilayer: Probed by Second Harmonic Generation. J Phys Chem B 2001. [DOI: 10.1021/jp0120918] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xiaoming Shang
- Department of Chemistry, Columbia University, New York, New York 10027
| | - Yan Liu
- Department of Chemistry, Columbia University, New York, New York 10027
| | - Elsa Yan
- Department of Chemistry, Columbia University, New York, New York 10027
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Zhigaltsev IV, Kaplun AP, Kucheryanu VG, Kryzhanovsky GN, Kolomeichuk SN, Shvets VI, Yurasov VV. LIPOSOMES CONTAINING DOPAMINE ENTRAPPED IN RESPONSE TO TRANSMEMBRANE AMMONIUM SULFATE GRADIENT AS CARRIER SYSTEM FOR DOPAMINE DELIVERY INTO THE BRAIN OF PARKINSONIAN MICE. J Liposome Res 2001; 11:55-71. [DOI: 10.1081/lpr-100103170] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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10
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Liu Y, Yan EC, Eisenthal KB. Effects of bilayer surface charge density on molecular adsorption and transport across liposome bilayers. Biophys J 2001; 80:1004-12. [PMID: 11159467 PMCID: PMC1301298 DOI: 10.1016/s0006-3495(01)76079-1] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Second harmonic generation (SHG) was used to study both the adsorption of malachite green (MG), a positively charged organic dye, onto liposomes of different lipid compositions, and the transport kinetics of MG across the liposome bilayer in real time. We found that the dye adsorption increased linearly with the fraction of negatively charged lipids in the bilayer. Similarly, the transport rate constant for crossing the bilayer increased linearly with the fraction of charged lipid in the bilayer.
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Affiliation(s)
- Y Liu
- Department of Chemistry, Columbia University, New York, New York 10027, USA
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11
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Pagliara A, Reist M, Geinoz S, Carrupt PA, Testa B. Evaluation and prediction of drug permeation. J Pharm Pharmacol 1999; 51:1339-57. [PMID: 10678488 DOI: 10.1211/0022357991777164] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
A major challenge confronting the pharmaceutical scientist is to optimize the selective and efficient delivery of new active entities and drug candidates. Successful drug development requires not only optimization of specific and potent pharmacodynamic activity, but also efficient delivery to the target site. Following advances in rational drug design, combinatorial chemistry and high-throughput screening techniques, the number of newly discovered and promising active compounds has increased dramatically in recent years, often making delivery problems the rate-limiting step in drug research. To overcome these problems, a good knowledge of the pharmacokinetic barriers encountered by bioactive compounds is required. This review gives an overview of the properties of relevant physiological barriers and presents some important biological models for evaluation of drug permeation and transport. Physicochemical determinants in drug permeation and the relevance of quantitative and qualitative approaches to the prediction and evaluation of passive drug absorption are also discussed.
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Affiliation(s)
- A Pagliara
- Institut de Chimie Thérapeutique, Université de Lausanne, Switzerland
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12
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Hwang SH, Maitani Y, Qi XR, Takayama K, Nagai T. Remote loading of diclofenac, insulin and fluorescein isothiocyanate labeled insulin into liposomes by pH and acetate gradient methods. Int J Pharm 1999; 179:85-95. [PMID: 10053205 DOI: 10.1016/s0378-5173(98)00392-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Remote loading of the model drugs diclofenac, insulin and fluorescein isothiocyanate labeled insulin (FITC-insulin) into liposomes by formation of transmembrane gradients were examined. A trapping efficiency of almost 100% was obtained for liposomal diclofenac, by the calcium acetate gradient method, whereas liposomes prepared by the conventional reverse-phase evaporation vesicle method had 1-8% trapping efficiencies. Soybean-derived sterol was a better stabilizer of the dipalmitoylphosphatidylcholine bilayer membrane than cholesterol, as shown from trapping efficiencies and drug release. The pH gradient method resulted in a 5-50% of FITC-insulin liposomal trapping efficiency, while insulin could not be loaded by this method. Liposomes released calcein in response to insulin, showing insulin interacts with the liposomal membrane in the presence of a transmembrane gradient. The present work has demonstrated a remote loading method for weak acids such as diclofenac into liposomes by the acetate gradient method. From the result of remote loading of FITC-insulin into liposomes by the pH gradient method, this method may be available for the preparation of liposomal peptides.
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Affiliation(s)
- S H Hwang
- Department of Pharmaceutics, Hoshi University, Ebara 2-4-41, Shinagawa-Ku, Tokyo 142-8501, Japan
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Wolfe C, Cladera J, O'Shea P. Amino acid sequences which promote and prevent the binding and membrane insertion of surface-active peptides: comparison of melittin and promelittin. Mol Membr Biol 1998; 15:221-7. [PMID: 10087509 DOI: 10.3109/09687689709044324] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The temporal sequence of molecular events involved in the interactions of a number of related peptides with membranes are revealed using two complementary fluorescence techniques. Comparative studies are reported of the interactions of melittin, promelittin and a melittin analogue with trp-19 replaced with Ile and the n-terminal gly replaced with a trp residue, with phosphatidylcholine membranes. It is shown that the interaction of the n-terminal region of melittin rapidly binds and inserts into the body of the membrane with a rate constant of around 367 s-1. This is followed by a slightly slower membrane insertion of the trp-19 region with a rate constant of around 112 s-1. The positive charges of the melittin molecule then come into close proximity with the membrane with rate constants around 27 s-1. Finally, these charged regions insert into the hydrophobic core of the membrane with rate constants of about 0.3 s-1. The effect of incorporating net negative charge onto the membrane surface in the form of 15 mole % phosphatidylserine, augments by about threefold, the binding of the charged domains of the melittin molecule. The observations of the melittin interactions are compared with the melittin-precursor protein, promelittin. Sections of the promelittin molecule are also found to bind and insert into the body of the phospholipid membrane, although nearly 30 times less rapidly than melittin. No charged sections of promelittin are found to insert into the membrane.
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Affiliation(s)
- C Wolfe
- Institute of Food Research, Norwich Research Park, UK
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14
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Males RG, Phillips PS, Herring FG. Equations describing passive transport through vesicular membranes. Biophys Chem 1998; 70:65-74. [PMID: 9474763 DOI: 10.1016/s0301-4622(97)00107-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A theoretical description of the kinetics of the passive transport of both lipophobic and lipophilic nonelectrolytes, weak acids, and weak bases through membranes of large unilamellar vesicles is discussed. Equations are derived which may be used to obtain permeability coefficients and predict the extent of LUV entrapment of permeant molecules. Theoretical curves are generated to illustrate the difference between lipophobic and lipophilic permeation. By applying a diffusional approach rather than a simple first order kinetic approach to the problem of passive transport, some of the inconsistencies observed in other works are corrected.
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Affiliation(s)
- R G Males
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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15
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Pagliara A, Carrupt PA, Caron G, Gaillard P, Testa B. Lipophilicity Profiles of Ampholytes. Chem Rev 1997; 97:3385-3400. [PMID: 11851494 DOI: 10.1021/cr9601019] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alessandra Pagliara
- Institut de Chimie thérapeutique, BEP, Université de Lausanne, CH-1015 Lausanne-Dorigny, Switzerland
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16
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Cullis PR, Hope MJ, Bally MB, Madden TD, Mayer LD, Fenske DB. Influence of pH gradients on the transbilayer transport of drugs, lipids, peptides and metal ions into large unilamellar vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1331:187-211. [PMID: 9325441 DOI: 10.1016/s0304-4157(97)00006-3] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- P R Cullis
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada.
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Interaction and translocation of cysteamine (mercaptoethylamine) with model membranes: a 15N-NMR and 1H-NMR study. Eur J Pharm Biopharm 1997. [DOI: 10.1016/s0939-6411(96)00012-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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18
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Reymond F, Steyaert G, Pagliara A, Carrupt PA, Testa B, Girault H. Transfer Mechanism of Ionic Drugs: Piroxicam as an agent facilitating proton transfer. Helv Chim Acta 1996. [DOI: 10.1002/hlca.19960790616] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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19
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Chakrabarti AC, Deamer DW. Permeation of membranes by the neutral form of amino acids and peptides: relevance to the origin of peptide translocation. J Mol Evol 1994; 39:1-5. [PMID: 8064865 DOI: 10.1007/bf00178243] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The flux of amino acids and other nutrient solutes such as phosphate across lipid bilayers (liposomes) is 10(5) slower than facilitated inward transport across biological membranes. This suggest that primitive cells lacking highly evolved transport systems would have difficulty transporting sufficient nutrients for cell growth to occur. There are two possible ways by which early life may have overcome this difficulty: (1) The membranes of the earliest cellular life-forms may have been intrinsically more permeable to solutes; or (2) some transport mechanism may have been available to facilitate transbilayer movement of solutes essential for cell survival and growth prior to the evolution of membrane transport proteins. Translocation of neutral species represents one such mechanism. The neutral forms of amino acids modified by methylation (creating protonated weak bases) permeate membranes up to 10(10) times faster than charged forms. This increased permeability when coupled to a transmembrane pH gradient can result in significantly increased rates of net unidirectional transport. Such pH gradients can be generated in vesicles used to model protocells that preceded and were presumably ancestral to early forms of life. This transport mechanism may still play a role in some protein translocation processes (e.g. for certain signal sequences, toxins and thylakoid proteins) in vivo.
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Affiliation(s)
- A C Chakrabarti
- Section of Molecular and Cellular Biology, University of California, Davis 95616
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20
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Chakrabarti AC. Permeability of membranes to amino acids and modified amino acids: Mechanisms involved in translocation. Amino Acids 1994; 6:213-29. [DOI: 10.1007/bf00813743] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/1993] [Accepted: 06/11/1993] [Indexed: 10/26/2022]
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