• Biomedical Science Letters
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• v.18 no.4
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• pp.329-337
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• 2012

${\alpha}$-synuclein (${\alpha}$-syn) is known to be implicated in the pathogenesis of Parkinson's disease and transiently bind to biological vesicles. In this study, we examined the effect of molecular crowding on the interaction of ${\alpha}$-syn with biological vesicles by using inert polymers since the environment of proteins in cells are crowded with other macromolecules. The addition of different polymers including polyethylene glycol, dextran, and ficoll enhanced the binding of ${\alpha}$-syn to vesicles in a concentration-dependent manner and the association of ${\alpha}$-syn with vesicle was proportionally augmented by increased expression of ${\alpha}$-syn. However, molecular crowding had a neglectable effect on the vesicle binding of ${\alpha}$-syn mutants (A30P, TG6), which has been reported to show impaired vesicle binding capacity. These results suggest that transient interaction of ${\alpha}$-syn with vesicles occurs more commonly in cells than expected implying interaction with vesicles may be one of the physiological processes in which ${\alpha}$-syn is involved.

• Journal of Microbiology
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• v.40 no.4
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• pp.319-326
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• 2002

Cellular DNA in prokaryotes is organized in nucleic acid-protein self-assemblies referred to as the nucleoid. The physical forces responsible for its stability inside the poor solvent properties of the cytoplasm and their functional implications are not understood. Studies on the organisation and functioning of the cytosol of cells largely rely on experimental protocols performed in highly dilute solutions using biochemically purified molecules, which is not a reliable substitute for the situation existing in vivo. Our current research interest is focused on the characterization of biological and physical forces determining the compaction and phase separation of DNA in Escherichia coli cytoplasm. We have emphasized the effect of excluded volume in solutions with high macromolecular concentrations (macromolecular crowding) upon self-association patterns of reactions. The prokaryotic cytosol was simulated by addition of inert polymer polyethylene glycol (PEG) (average molecular weight 20000), as an agent which afterwards facilitates the self-association of macromolecules. Fluorescence microscopy was used for direct visualization of nucleoids in intact cells, after staining with DAPI (4',6-diamidino-2-phenylindole dihydrochloride). Addition of the crowding agent PEG 20,000, in increasing concentrations generated progressively enhanced nucleoid compaction, the effect being stronger in the presence of 0.2 M NaCl and 5 mM MgCl$\_$2/. Under these conditions, the nucleoids were compacted to volumes of around 2 ㎛$\^$3/ or comparable sizes with that of living cells.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.307-310
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• 2007

We describe effects of ionic and neutral additives on phase and structural behavior of the lyotropic chromonic liquid crystals used in preparation of optical elements such as polarizers and compensators.

• Journal of the Korean Chemical Society
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• v.34 no.3
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• pp.239-247
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• 1990

The gas-phase S_N2$ reactions can be classified into neutral bimolecular, solvated, and ionic reactions; the neutral bimolecular reaction proceeds via retention mechanism whereas the ionic reaction produces inversion products. In the reaction of solvated nucleophile with one solvent molecule, a six-center transition state (TS) is formed and the two processes i.e., retention and inversion, are found to compete with a favored path depending on the electronic effect of the nucleophile and substituents in the substrate and on the steric requirement. In the ionic reaction, the difference in the energy barrier between the two processes reduces to a small value when the substrate methyl group is made bulky, leaving ability of the leaving group is improved and at the same time the negative charge of the nucleophile is dispersed. When the reaction center atom in the $S_N2$ reaction is changed to a larger sized second row elements, the activation barrier decreases since the steric crowding in the penta-coordinated TS is relieved. However within the same row, the barrier was found to increase as the atomic size decreased. For the boron, B, the barrier height was the least since in addition to the relatively large atomic size compared to C and N, it forms tetra-coordinated TS so that the steric crowding becomes nearly negligible.

• Journal of Life Science
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• v.26 no.8
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• pp.881-886
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• 2016

Cephalanthera erecta (Thunb. ex, Murray) is an herbaceous and a member of the genus Cephalanthera in the family Orchidaceae. The species is an herbaceous and has reputed Chinese medicinal value. It has been investigated the population density and spatial distribution of this species at Mt. Ahop in Korea during 2015. The spatial pattern of C. erecta was analyzed according to several patchiness indexes, population uniformity or aggregation under different sizes of plots by dispersion indices, and spatial autocorrelation. The mean crowding (M*) and patchiness index (PAI) showed positive values except one small plot (2 m × 2 m). Most natural individuals of C. erecta for plots were not uniformly distributed in the forest community. The small plots (2 m × 2 m, to 8 m × 16 m) of C. erecta were uniformly distributed in the forest community and large plots (16 m × 16 m and 16 m × 32 m) were aggregately distributed. Significant aggregations by Moran's I of C. erecta were partially observed within IV classes (12 m). Dissimilarity among pairs of individuals could found by more than 18.0 m. In conclusion, the geographic distribution of C. erecta is not even with varying degrees of size of plots and human activities give rise to density effects in the plots at Mt. Ahop in Korea.