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Affiliation(s)
- William D. Lubell
- Editorial Board, Peptide Science , Département de chimie; Université de Montréal; Montréal Canada
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El-Khouly ME, Lee SH, Kay KY, Fukuzumi S. Synthesis and fast electron-transfer reactions of fullerene–carbazole dendrimers with short linkages. NEW J CHEM 2013. [DOI: 10.1039/c3nj00770g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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El-Khouly ME, Han KJ, Kay KY, Fukuzumi S. Stabilization of the Charge-Separated States of Covalently Linked Zinc Porphyrin-Triphenylamine-[60]Fullerene. Chemphyschem 2010; 11:1726-34. [DOI: 10.1002/cphc.200900885] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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El-Khouly M, Kim J, Kay KY, Choi C, Ito O, Fukuzumi S. Synthesis and Photoinduced Intramolecular Processes of Light-Harvesting Silicon Phthalocyanine-Naphthalenediimide-Fullerene Connected Systems. Chemistry 2009; 15:5301-10. [DOI: 10.1002/chem.200900165] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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SHIMIZU TOSHIMI, TANAKA YOSHIO, TSUDA KEISHIRO. Selective ion transport and ion extraction by synthetic cyclic octapeptide. ACTA ACUST UNITED AC 2009. [DOI: 10.1111/j.1399-3011.1986.tb01026.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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El-Khouly ME, Shim SH, Araki Y, Ito O, Kay KY. Effect of Dual Fullerenes on Lifetimes of Charge-Separated States of Subphthalocyanine−Triphenylamine−Fullerene Molecular Systems. J Phys Chem B 2008; 112:3910-7. [DOI: 10.1021/jp7108658] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Mohamed E. El-Khouly
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai, 980-8577 Japan, Department of Chemistry, Faculty of Education, Kafr El-Sheikh University, Egypt, and Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
| | - Sun Hee Shim
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai, 980-8577 Japan, Department of Chemistry, Faculty of Education, Kafr El-Sheikh University, Egypt, and Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
| | - Yasuyuki Araki
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai, 980-8577 Japan, Department of Chemistry, Faculty of Education, Kafr El-Sheikh University, Egypt, and Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
| | - Osamu Ito
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai, 980-8577 Japan, Department of Chemistry, Faculty of Education, Kafr El-Sheikh University, Egypt, and Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
| | - Kwang-Yol Kay
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai, 980-8577 Japan, Department of Chemistry, Faculty of Education, Kafr El-Sheikh University, Egypt, and Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
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de la Torre G, Giacalone F, Segura JL, Martín N, Guldi DM. Electronic communication through pi-conjugated wires in covalently linked porphyrin/C60 ensembles. Chemistry 2006; 11:1267-80. [PMID: 15635684 DOI: 10.1002/chem.200400604] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Novel photo- and electroactive triads, in which pi-conjugated p-phenylenevinylene oligomers (oPPVs) of different length are connected to a photoexcited-state electron donor (i.e., zinc tetraphenylporphyrin) and an electron acceptor (i.e., C(60)), were designed, synthesized, and tested as electron-transfer model systems. A detailed physicochemical investigation, concentrating mainly on long-range charge separation and charge recombination and kinetics, revealed small attenuation factors beta of 0.03+/-0.005 A(-1). Energy matching between the HOMO levels of C(60) and oPPVs emerged as a key parameter for supporting molecular-wire-like behavior: It favors rapid and efficient electron or hole injection into the oPPV wires. Large electronic coupling values were determined as a result of paraconjugation in the oPPV moieties.
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Affiliation(s)
- Gema de la Torre
- Departamento Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040-Madrid, Spain
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Guldi DM, Giacalone F, de la Torre G, Segura JL, Martín N. Topological Effects of a Rigid Chiral Spacer on the Electronic Interactions in Donor–Acceptor Ensembles. Chemistry 2005; 11:7199-210. [PMID: 16163762 DOI: 10.1002/chem.200500209] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Two triads (donor-spacer-acceptor), exTTF-BN-C60 (6) and ZnP-BN-C60 (7), in which electron donors (i.e., exTTF or ZnP) are covalently linked to C60 through a chiral binaphthyl bridge (BN), have been prepared in a multistep synthetic procedure starting from a highly soluble enantiomerically pure binaphthyl building block (1). Unlike other oligomeric bridges, with binaphthyl bridges, the conjugation between the donor and the acceptor units is broken and geometric conformational changes are facilitated. Consequently, distances and electronic interactions between the donor and C60 are drastically changed. Both donor-spacer-acceptor (D-s-A) systems (i.e., 6 and 7) exhibit redox processes that correspond to all three constituent electroactive units, namely, donor, BN, and C60. Appreciable differences were, however, observed when comparing triad 6, in which no significant exTTF-C60 interactions were noted, with D-s-A 7, whose geometry favors donor-acceptor and pi-pi interactions that result in ZnP-C60 electronic communication. This through-space interaction is, for example, reflected in the redox potentials. Excited-state studies, carried out by fluorescence and transient absorption spectroscopy, also support through-space rather than through-bond interactions. Although both triads form the corresponding radical-ion pair, that is, exTTF*+-BN-C60*- and ZnP*+-BN-C60*-, dramatic differences were found in their lifetimes: 165 micros and 730 ns, respectively.
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Affiliation(s)
- Dirk M Guldi
- Institute for Physical and Theoretical Chemistry, University of Erlangen, 91058 Erlangen, Germany.
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Feng Y, Melacini G, Taulane JP, Goodman M. Collagen-based structures containing the peptoid residue N-isobutylglycine (Nleu): Synthesis and biophysical studies of Gly-Pro-Nleu sequences by circular dichroism, ultraviolet absorbance, and optical rotation. Biopolymers 1998. [DOI: 10.1002/(sici)1097-0282(199612)39:6<859::aid-bip10>3.0.co;2-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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11
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Feng Y, Melacini G, Taulane JP, Goodman M. Collagen-based structures containing the peptoid residue N-isobutylglycine (Nleu): synthesis and biophysical studies of Gly-Pro-Nleu sequences by circular dichroism, ultraviolet absorbance, and optical rotation. Biopolymers 1996; 39:859-72. [PMID: 8946805 DOI: 10.1002/(sici)1097-0282(199612)39:6%3c859::aid-bip10%3e3.0.co;2-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A peptoid residue N-isobutylglycine (Nleu) was introduced as a proline surrogate in collagen-like triple helical structures. A series of single chain and template-assembled collagen-based peptide-peptoid structures composed of Gly-Pro-Nleu sequences were prepared by solid-phase segment condensation methods. Both a synthetic route in solution and a solid phase method were employed to couple the KTA (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, also known as the Kemp triacid) based template, KTA-(Gly-OH)3, to peptide-peptoid chains. Biophysical studies using CD, uv absorbance, and optical rotation measurements demonstrated that these compounds form triple-helical structures when the chains are longer than critical lengths. Results from melting curve measurements indicated that the Gly-Pro-Nleu sequence is comparable to the Gly-Pro-Pro sequence in stabilizing a triple-helical conformation. The KTA-based template stabilized triple-helical structures as can be seen by the increased melting temperatures as compared to equivalent single chain molecules. In addition, the template reduced the minimum chain length necessary to form a triple helix from six to only three trimer repeats.
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Affiliation(s)
- Y Feng
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla 92093-0343, USA
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12
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Using cyclic peptide mixtures as probes for metal ion host-guest interactions. ACTA ACUST UNITED AC 1996. [DOI: 10.1007/bf00131081] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Nishino N, Shiroishi T, Muraoka T, Fujimoto T. Lipophilic Cyclic Hexapeptide for Calcium Ion-Selective-Electrode. CHEM LETT 1992. [DOI: 10.1246/cl.1992.665] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Deber CM, Glibowicka M, Woolley GA. Conformations of proline residues in membrane environments. Biopolymers 1990; 29:149-57. [PMID: 2328283 DOI: 10.1002/bip.360290120] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Although noted as hydrophilic residues with helix-breaking potential, proline residues are observed in putatively alpha-helical transmembrane (TM) segments of many channel-forming integral membrane proteins. In addition to the recognized property of X-Pro peptide bonds (where X = any amino acid) to occur in cis as well as trans isomeric states, the tertiary amide character of the X-Pro bond confers increased propensity for involvement of its carbonyl group in specific H-bonded structures (e.g., beta- and gamma-turns) and/or liganding interactions with positively charged species. To examine this latter situation in further detail, we identified Leu-Pro-Phe as a consensus sequence triad based on actual occurrences of intramembranous Pro residues in transport protein TM segments. Accordingly, we have undertaken the synthesis of hydrophobic peptides with potential membrane affinity, of which t-butyloxycarbonyl-L-Ala-L-Ala-L-Ala-L-Leu-L-Pro-L-Phe-OH (t-Boc-AAALPF-OH) is an initial compound. Partitioning of this peptide into model membrane environments composed of lipid micelles induces specific conformation(s) for the membrane-bound hexapeptide, as monitored by 75-MHz 13C-nmr spectral behavior of 13C-enriched Leu and Pro carbonyl carbons, and by 300-MHz 1H-nmr spectra of peptide alpha, beta, and aromatic protons. Data are interpreted in terms of an intramolecularly H-bonded inverse gamma-turn conformation in the membrane environment involving the Leu-Pro-Phe triad. The inherent structural instability of a Pro-containing segment in a TM helix due to the multiplicity of possible local conformations is discussed as a functional aspect of membrane-buried prolines in transport proteins.
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Affiliation(s)
- C M Deber
- Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada
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Ozeki E, Kimura S, Imanishi Y. Conformation and complexation with metal ions of cyclic hexapeptides: cyclo (L-Leu-L-Phe-L-Pro)2 and cyclo [L-Cys(Acm)-L-Phe-L-Pro]2. INTERNATIONAL JOURNAL OF PEPTIDE AND PROTEIN RESEARCH 1989; 34:111-7. [PMID: 2807727 DOI: 10.1111/j.1399-3011.1989.tb01498.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cyclic hexapeptides, cyclo (L-Leu-L-Phe-L-Pro)2 and cyclo[L-Cys(Acm)-L-Phe-L-Pro]2, in which Acm represents an acetoamide-methyl group, were synthesized, and the conformation and complexation with metal ions were investigated. Cooperation of the carbonyl groups of the Cys(Acm) side chains with those of the cyclic skeleton in complexation was especially examined. Cyclo(L-Leu-L-Phe-L-Pro)2, which possesses no functional groups on side chains, was taken as the reference compound. 13C- and two-dimensional n.m.r. measurements revealed that cyclo(L-Leu-L-Phe-L-Pro)2 and cyclo[L-Cys(Acm)-L-Phe-L-Pro]2 took a C2-symmetric conformation containing cis L-Phe-L-Pro bonds in chloroform and acetonitrile. Both cyclic hexapeptides were found to complex selectively with Ba2+ and Ca2+ in acetonitrile. On complexation the conformation of either cyclic hexapeptide changed into a similar one. However, the binding constant of cyclo[L-Cys(Acm)-L-Phe-L-Pro]2 was higher than that of cyclo(L-Leu-L-Phe-L-Pro)2. The n.m.r. measurements showed that the amide carbonyl groups of Cys(Acm) side chains as well as those of cyclic skeleton in cyclo[L-Cys(Acm)-L-Phe-L-Pro]2 cooperatively bound the cations.
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Affiliation(s)
- E Ozeki
- Department of Polymer Chemistry, Kyoto University, Japan
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Kimura S, Ozeki E, Imanishi Y. Ca2+ binding cyclic octapeptides having an alternating Sar and a hydrophobic amino acid in the sequence. Biopolymers 1989; 28:1235-46. [PMID: 2775838 DOI: 10.1002/bip.360280705] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cyclic octapeptides having alternating Sar and hydrophobic amino acid sequences, such as cyclo[Lys(Z)-Sar-Leu-Sar-Leu-Sar-Leu-Sar] (C8KL), cyclo[Glu(OMe)-Sar-Lys(Z)-Sar-Leu-Sar-Leu-Sar] (C8KE, and cyclo[Lys(Suc)-Sar-Leu-Sar-Leu-Sar-Leu-Sar] [C8K(Suc)L, Suc represents succinic acid], were synthesized. These cyclic octapeptides formed a complex selectively with Ca2+. Upon complexation, trans peptide bonds of Sar residues were isomerized to cis peptide bonds. C8KL and C8KE showed very similar characteristics of Ca2+ binding, extraction of Ca2+ from an aqueous solution to a chloroform solution, and Ca2+ transport through a liquid chloroform membrane. C8KL transported Ca2+ across the lipid bilayer membrane above the phase-transition temperature, while C8KE and C8K(Suc)L did not. Therefore, the transport of Ca2+ through the lipid bilayer membrane is very sensitive to the hydrophobicity of the carrier molecule.
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Ion transport, ion extraction, and ion binding by synthetic cyclic octapeptide. J INCL PHENOM MACRO 1987. [DOI: 10.1007/bf00656411] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Deber CM, Hsu LC. Calcium transport by ionophorous peptides in dog and human lymphocytes detected by quin-2 fluorescence. Biochem Biophys Res Commun 1986; 134:731-5. [PMID: 3947349 DOI: 10.1016/s0006-291x(86)80481-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Synthetic peptides of structure cyclo(Glu(OBz)-Sar-Gly-(N-R)Gly)2 (I), electrogenic Ca2+-selective carriers in phospholipid vesicle membranes, are shown to mediate the uptake of Ca2+ ions into the cytoplasm of dog and human lymphocytes. Ca2+ transport by DECYL-2E (I, R = n-decyl) - monitored by measurements of the fluorescence of an intracellular dye, quin-2 - occurred at a rate comparable to that produced by electroneutral Ca2+ ionophores ionomycin and Br-A23187. Fluorescence quenching experiments using Mn2+ suggested a greater selectivity by DECYL-2E for Ca2+/Mn2+ vs. the other two ionophores. The result that Ca2+ ions can traverse biological membranes bound in a neutral cavity consisting exclusively of peptide carbonyl ligands may imply the functional significance of binding sites of similar structures in membrane transport proteins.
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Shimizu T, Tanaka Y, Tsuda K. Cation-binding Properties of Ionophorous Cyclic Octapeptide in Acetonitrile Solution. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1985. [DOI: 10.1246/bcsj.58.3436] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Ueno K, Shimizu T. Crystal structure and conformation of a cyclic tetrapeptidecyclo(L-Pro-Sar)2 containing all-cis peptide units. Biopolymers 1983. [DOI: 10.1002/bip.360220208] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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May PM, Bulman RA. The present status of chelating agents in medicine. PROGRESS IN MEDICINAL CHEMISTRY 1983; 20:225-336. [PMID: 6356226 DOI: 10.1016/s0079-6468(08)70220-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Shimizu T, Tanaka Y, Tsuda K. Conformational Studies of Bis(cyclic tetrapeptide),S,S′-Bis[cyclo(Gly–L-hemiCys–Sar–L-Pro)]. A Proposed Castanet-type Structure in a Dimethyl Sulfoxide Solution. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1982. [DOI: 10.1246/bcsj.55.3808] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Drobnies AE, Deber CM. Cation transport properties of a synthetic Ca2+-selective peptide ionophore in phospholipid and sarcoplasmic reticulum vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 691:30-6. [PMID: 6128028 DOI: 10.1016/0005-2736(82)90210-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Transport by the synthetic cyclic peptide ionophore CYCLEX-2E (Deber, C.M. Young, M.E.M., and Tom-Kun, J. (1980) Biochemistry 19, 6194-6198), which in contrast to Ca2+ ionophore A23187 contains no ionizable protons, has been studied with respect to Ca2+ and Na+ transport, and the involvement of exchanged, or counter-transported ions during the transport process. CYCLEX-2E was found to equilibrate Na+ and Ca2+ gradients across phospholipid vesicle membranes. Experiments using the indicator dye Arsenazo III established that calcium ions were indeed reaching the aqueous intravesicular compartments. Absence of metal cations in the external buffer slowed, but did not eliminate, the efflux of Ca2+ from phosphatidylcholine vesicles. As an example of its activity in a biological membrane, CYCLEX-2E was shown to be capable of producing Ca2+ efflux from sarcoplasmic reticulum vesicles which has been loaded with Ca2+ in an ATP-dependent manner. The overall results suggest that in transport by synthetic peptide ionophores typified by CYCLEX-2E, electroneutrality is achieved either through (a) peptide-mediated compensating (but not coupled) fluxes of other cations, or where this is not an option, by (b) transmembrane diffusion of permeant ions such as H+, OH-, or Cl-.
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Ptak M, Heitz A, Guinand M, Michel G. 400 MHz 1H n.m.r. study of the conformation and self-association of peptidolipin NA. Int J Biol Macromol 1982. [DOI: 10.1016/0141-8130(82)90030-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Gomperts BD, Bennett JP, Allan D. A synthetic ionophore for Ca2+: studies with model and biological systems. EUROPEAN JOURNAL OF BIOCHEMISTRY 1981; 117:559-62. [PMID: 6169522 DOI: 10.1111/j.1432-1033.1981.tb06373.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We show that the relatively simple beta-diketone, 1.1.1.2.2.3.3-heptafluoro-7,7-dimethyloctane-4,6-dione, known as "fod", will solvate Ca2+ ions in an organic phase. In consequence it will transport Ca2+ across phospholipid bilayers. It acts as predicted for a Ca2+-transporting ionophore in two biological systems: it will stimulate Ca2+-dependent K+ efflux from human red blood cells, and Ca2+-dependent histamine secretion from rat peritoneal mast cells.
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Deber CM, Young ME, Tom-Kun J. Synthetic cation transport peptides: calcium transport across phospholipid membranes. Biochemistry 1980; 19:6194-8. [PMID: 7470459 DOI: 10.1021/bi00567a038] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Molecular aspects of peptide-mediated calcium transport are examined through the study of the cation transport properties of a series of synthetic cyclic octapeptides. These peptides, of general structure cyclo[Glu(OR1)-Sar-Gly-(N-R2)Gly]2 (R1 = H or benzyl ester; R2 = cyclohexyl, n-hexyl, or n-decyl) (and an Asp analogue), contain central binding cavities of geometry and dimensions similar to calcium-binding sites in proteins. Transport in Pressman cells ("thick liquid membranes") demonstrated the ionophorous activity of the synthetic peptides; among physiologically abundant cations, the order of selectivity was Ca2+ greater than Na+, K+ much greater than Mg2+. Cation competition studies further showed that cyclo[Glu(OBz)-Sar-Gly-(N-cyclohexyl)Gly]2 (CYCLEX-2E) is essentially a calcium-specific transport peptide whenever calcium is present. When the CYCLEX-2E peptide was added to a suspension of 45Ca2+-loaded sonicated phosphatidylcholine (PC) vesicles in a dialysis sac, the vesicles were completely emptied of internal calcium. Controls using [14C]sucrose established that CYCLEX-2E caused no nonspecific membrane damage. Calcium efflux experiments using several salts of calcium (including 36C1-, [14C]acetate, [14C]succinate, and 35SO4(2-)) suggested that these anions do not specifically accompany the Ca2+-peptide active transporting species across the phospholipid membrane. However, when 45Ca2+-loaded PC vesicles were suspended in mental-free buffer and treated with CYCLEX-2E peptide, calcium efflux did not occur until calcium or sodium chloride was added to the external medium.
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