Search results for "Trimer"
showing 10 items of 76 documents
Localization of the N-terminal Domain in Light-harvesting Chlorophyll a/b Protein by EPR Measurements
2005
The conformational distribution of the N-terminal domain of the major light-harvesting chlorophyll a/b protein (LHCIIb) has been characterized by electron-electron double resonance yielding distances between spin labels placed in various domains of the protein. Distance distributions involving residue 3 near the N terminus turned out to be bimodal, revealing that this domain, which is involved in regulatory functions such as balancing the energy flow through photosystems (PS) I and II, exists in at least two conformational states. Models of the conformational sub-ensembles were generated on the basis of experimental distance restraints from measurements on LHCIIb monomers and then checked f…
Thermal stability of trimeric light-harvesting chlorophyll a/b complex (LHCIIb) in liposomes of thylakoid lipids.
2006
The major light-harvesting chlorophyll a/b complex (LHCIIb) of photosystem (PS) II functions by harvesting light energy and by limiting and balancing the energy flow directed towards the PSI and PSII reaction centers. The complex is predominantly trimeric; however, the monomeric form may play a role in one or several of the regulatory functions of LHCIIb. In this work the dissociation temperature was measured of trimeric LHCIIb isolated from Pisum thylakoids and inserted into liposomes made of various combinations of thylakoid lipids at various protein densities. Dissociation was measured by monitoring a trimer-specific circular dichroism signal in the visible range. The LHCIIb density in t…
Cooperative mechanism for anchoring highly polar molecules at an ionic surface
2009
Structure formation of the highly polar molecule cytosine on the (111) cleavage plane of calcium fluoride is investigated in ultrahigh vacuum using noncontact atomic force microscopy at room temperature. Molecules form well-defined trimer structures, covering the surface as homogeneously distributed stable structures. Density-functional theory calculations yield a diffusion barrier of about 0.5 eV for individual molecules suggesting that they are mobile at room temperature. Furthermore, it is predicted that the molecules can form trimers in a configuration allowing all molecules to attain their optimum adsorption position on the substrate. As the trimer geometry facilitates hydrogen bonding…
Decoupling the artificial special pair to slow down the rate of singlet energy transfer
2012
Trimer 2, composed of a cofacial heterobismacrocycle, octamethyl-porphyrin zinc(II) and bisarylporphyrin zinc(II) held by an anthracenyl spacer, and a flanking acceptor, bisarylporphyrin free-base ( Ar = -3,5-(t Bu )2 C 6 H 3), has been studied by means of absorption spectroscopy, "steady state and time-resolved fluorescence" and fs transient absorption spectroscopy, and density functional theory (DFT) in order to assess the effect of decoupling the chromophores' low energy MOs on the rate of the singlet, S1, energy transfer, k ET , compared to a recently reported work on a heavily coupled trimeric system, Trimer 1, [biphenylenebis(n-nonyl)porphyrin zinc(II)]-bisarylporphyrin free-base ( A…
Structure and Magnetic Properties of the Ferromagnetic Cu3Cl126- Trimer in [(NH3C2H4)3NH]2Cu3Cl14
2004
The crystal structure consists of a strongly hydrogen bonded network of tris(N-ethylammonium)ammonium cations, Cu3Cl12(6)- trimeric species, and Cl- anions. The Cu3Cl12(6)- trimers are formed by two distorted tetrahedral CuCl4(2)- anions linked to a central square planar CuCl4(2)- anion via semicoordinate Cu-Cl...Cu mu1 bridges. The central copper ion shows only small deviations from ideal D4h symmetry, while the terminal copper ions show a mild distortion from D2d symmetry with an average trans Cl-Cu-Cl angle of 136.0 degrees. The semicoordinate linkages provide a ferromagnetic exchange pathway between the copper ions with J/k = 6.91(3) K. Short Cl...Cl contacts (3.67-3.90 angstoms) lead t…
Decay pathway determination of even-size dicationic silver clusters: Ag162+ and Ag182+ revisited by pre-precursor selection and sequential decay
2000
Abstract It is demonstrated how by selection of pre-precursor cluster ions Ag 2 n +1 2+ and collision-induced dissociation an ensemble of Ag 2 n 2+ can be produced, which is not contaminated by Ag n + clusters of the same size-to-charge state ratio, n / z . By use of this technique, Ag 16 2+ and Ag 18 2+ precursor ensembles have been prepared for further investigations. They are observed to decay by neutral monomer evaporation, Ag 2 n 2+ →Ag 2 n −1 2+ +Ag, and trimer fission, Ag 2 n 2+ →Ag 2 n −3 + +Ag 3 + , and show no sign of symmetric fission.
Binuclear Ni(II) complexes based on bridging oxalate and tetracyanometallates.
2002
The trimeric complexes, [{Ni(dien)}2(m-ox){(m-Pd(CN)4)}] (2) and [{Ni(dien)}2(m-ox){(m-Pt(CN)4)}] (3) were synthesised by the reaction of [{Ni(dien)(H2O)}2(m-ox)](PF6)2/2H2O (dien � /dietylenetriamine and ox� /oxalate) with K2Pd(CN)4 and K2Pt(CN)4, respectively. In this reaction, water substitution and molecular reconstruction reactions take place to afford trimer complexes. These compounds are isostructural with the molecular compound [{Ni(dien)}2(m-ox){(m-Ni(CN)4)}] (1). In each complex, the two octahedrally coordinated Ni atoms are oxalate bridged and the sphere of coordination of each Ni is completed by three nitrogen atoms from a diethylenetriamine ligand in fac arrangement and one nit…
Syntheses and catalytic oxotransfer activities of oxo molybdenum(vi) complexes of a new aminoalcohol phenolate ligand.
2017
The new aminoalcohol phenol 2,4-di-tert-butyl-6-(((2-hydroxy-2-phenylethyl)amino)methyl)phenol (H2L) was prepared by a facile solvent-free synthesis and used as a tridentate ligand for new cis-dioxomolybdenum(vi)(L) complexes. In the presence of a coordinating solvent (DMSO, MeOH, pyridine), the complexes crystallise as monomeric solvent adducts while in the absence of such molecules, a trimer with asymmetric Mo[double bond, length as m-dash]O→Mo bridges crystallises. The complexes can catalyse epoxidation of cis-cyclooctene and sulfoxidation of methyl-p-tolylsulfide, using tert-butyl hydroperoxide as oxidant.
Palmitoylation of Endothelin Receptor A
1996
Post-translational modifications such as phosphorylation and palmitoylation play important roles for the function and regulation of receptors coupled to heterotrimeric guanyl nucleotide-binding proteins. Here we demonstrate that the human endothelin receptor A (ETA) incorporates [3H]palmitate. Mutation of a cluster of five cysteine residues present in the cytoplasmic tail of ETA into serine or alanine residues completely prevented palmitoylation of the receptor. The ligand binding affinity of the non-palmitoylated ETA mutants was essentially unchanged as compared to the palmitoylated wild type ETA suggesting that the replacement of the cysteine residues did not alter the overall structure o…
Chapter 17 Muscarinic receptors and cell signalling
1996
Publisher Summary Cells have developed signal transduction mechanisms in order to communicate with the cell exterior. Acetylcholine as an external signal is recognized by nicotinic and muscarinic receptors. This chapter presents various muscarinic receptors belonging to the superfamily of G protein-coupled receptors consisting of seven transmembrane (TM) helices tightly packed in a ring-like structure and arranged in a counter-clockwise fashion. Agonist binding leads to a conformational change of the receptor, thereby activating associated G proteins. Muscarinic stimulation of G proteins leads to the activation or inhibition of ion channels, such as K + and Ca 2+ channels, the activation of…