• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.52-62
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• 1990

Cationic polycarbonate type polyurethane was prepared from the quaternization reaction of N-methyldiethanolamine(MDEA) in urethane backbone which was obtained from the reaction of polycarbonate polyol, MDI and MDEA(chain exetender). Tensile strength and modulus of the cationic urethane resins were increased sharply with increasing the ionic content in urethane backbone. But hydrolysis resistance was decreased with increasing ionic contents. The selectivity of the cationic polycabonate urethane membrane for water/ethanol separation by pervaporation was about 20. The carrier mediated transport mechanism was considered the most probable separation mechanism for these membranes.

• Applied Biological Chemistry
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• v.26 no.2
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• pp.125-131
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• 1983

Formal net charges, bond populations, atomic orbital coefficients, energy components and conformation of dimethyl-2,2-dichlorovinylphosphate have been studied theoretically by using the CNDO/2 molecular orbital calculation method in attempt to describe the reactivity and the stability of the molecule. From the analysis of rate equation, molecular orbital calculations and identification of the hydrolysis products, 2,2-dichloroacetaldehyde and dimethylphosphoric acid, a mechanism of the hydrolysis of dimethyl-2,2-dichlorovinylphosphate(DDVP) has been proposed. The hydrolysis of DDVP proceeds through the mechanism of nucleophilic addition, typical Micheal reaction in basic media. Therefore, it appears probable that the attack by strong nucleophile, hydroxide ion occurs at the increased positive charge $C_2({\alpha})$ atom of a staggered conformation due to the inductive effect (-)I>(+)R of 2,2-dichlorovinyl, electron-attracting group. And then, the hydrolytic scission involves the $C_2({\alpha})-O_3$, ${\pi}-anti-bonding\;orbital({\pi}^*)$ in the subsequent reaction in aqueous solution.

• Journal of Korean Society of Forest Science
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• v.79 no.4
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• pp.376-387
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• 1990

A research effort has been made to determine soil buffer capacity in forest soils nearby urban and industrialized regions. Buffer capacities of soils from four regions were measured by different pH levels of artificial acid precipitation. The following conclusions have been drawn in response to the overall research objectives. Soil Suffer capacity was the highest in Kangwondo followed by Uisan, Yeochon and Seoul when simulated acid precipitation were treated at the level of pH 3.0-5.7. With the acid precipitation treatment below pH 2.0 level, however, the capacity dropped seriously with no significant differences between the regions. In Kangwondo region soils weathered from granite and limestone showed significant differences in the buffer capacities. Soil collected in Seoul and Ulsean revealed that the capacities tended to increase with the distance from the pollution sources when treated at pH 3.0, 4.5 and 5.7 level of acid precipitation. The major mechanism of soil buffer observed during simulated acid precipitation experiment was canon exchange for Kangwondo forest soils. In Seoul region canon exchange also played an important role in soil buffering under artificial acid precipitation between 3.0 and 5.7 pH levels, yet under pH 2.0 level aluminum and silicate hydrolysis. In Ulsan canon exchange was a msjor determinant for the buffer capacity above pH 4.5 level, between pH 3.0-4.5 aluminum hydrolysis and below pH 3.0 aluminum and silicate hydrolysis. In Yeochon silicate hydrolysis led buffer capacity above pH 4.5 and below pH 4.5 aluminum hydrolysis.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.473-478
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• 2000

The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

• Genomics & Informatics
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• v.6 no.1
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• pp.44-49
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• 2008

Protein kinase C (PKC) is a family of kinases involved in the transduction of cellular signals that promote lipid hydrolysis. PKC plays a pivotal role in mediating cellular responses to extracellular stimuli involved in proliferation, differentiation and apoptosis. Comparative analysis of the PKC-${\alpha},{\beta},{\varepsilon}$ isozymes of 200 recently sequenced microbial genomes was carried out using variety of bioinformatics tools. Diversity and evolution of PKC was determined by sequence alignment. The ser/thr protein kinases of Streptomyces coelicolor A3 (2), is the only bacteria to show sequence alignment score greater than 30% with all the three PKC isotypes in the sequence alignment. S.coelicolor is the subject of our interest because it is notable for the production of pharmaceutically useful compounds including anti-tumor agents, immunosupressants and over two-thirds of all natural antibiotics currently available. The comparative analysis of three human isotypes of PKC and Serine/threonine protein kinase of S.coelicolor was carried out and possible mechanism of action of PKC was derived. Our analysis indicates that Serine/ threonine protein kinase from S. coelicolor can be a good candidate for potent anti-tumor agent. The presence of three representative isotypes of the PKC super family in this organism helps us to understand the mechanism of PKC from evolutionary perspective.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.2
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• pp.128-136
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• 2004

The overall objective of this research was to find out the role of rapid mixing conditions in the species of hydrolyzed Al(III) formed by different Al(III) coagulants. When an Al(III) salt is added to water, monomers, polymers, or solid precipitates may form. Different Al(III) coagulants (alum and PACl) show to have different Al species distribution over a rapid mixing condition. During the rapid mixing period, for alum, formation of dissolved Al(III) (monomer and polymer) increases, but for PACl, precipitates of $Al(OH)_{3(s)}$. increases rapidly. Also, for alum, higher mixing speed favoured Al(III) polymers formation over precipitates of $Al(OH)_{3(s)}$ but for PACl, higher mixing speed formed more precipitates of $Al(OH)_{3(s)}$. At A/D and sweep condition, both $Al(OH)_{3(s)}$ and dissolved Al(III) (monomer and polymer) exist, concurrent reactions by both mechanism appear to cause simultaneous precipitation.

• Journal of Pharmaceutical Investigation
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• v.36 no.5
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• pp.315-320
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• 2006

Silymarin showed P-glycoprptein(P-gp) inhibitory activity as much as verapamil, a well-known P-gp inhibitor, by decreasing $IC_{50}$ value of daunomycin(DNM)($16.0{\pm}0.7{\mu}M$), increasing the DNM accumulation($224.9{\pm}3.2%$), and decreasing DNM efflux($58.5{\pm}6.7%$), concurrently. In this study, we clarified the mechanism of action of silymarin for P-gp inhibitory function. First, silymarin may bind to the ATP-binding site and thus, prevent ATP hydrolysis. Second, the P-gp inhibitory activity of silymarin is not related to changing the cellular P-gp level. Third, the cytotoxicity of silymarin was increased in the presence of verapamil, reflecting that silymarin is a competent P-gp substrate against verapamil in the P-gp-overexpressed adriamycin-resistant MCF-7 breast cancer(MCF-7/ADR) cells. Conclusively, silymarin had the P-gp inhibitory activity through the action of competent binding to the P-gp substrate-binding site. Therefore, silymarin can be a good candidate for safe and effective MDR reversing agent in clinical chemotherapy by administering concomitantly with anticancer drugs.

• BMB Reports
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• v.38 no.3
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• pp.266-274
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• 2005

High temperature requirement A (HtrA) and its homologues constitute the HtrA familiy proteins, a group of heat shock-induced serine proteases. Bacterial HtrA proteins perform crucial functions with regard to protein quality control in the periplasmic space, functioning as both molecular chaperones and proteases. In contrast to other bacterial quality control proteins, including ClpXP, ClpAP, and HslUV, HtrA proteins contain no regulatory components or ATP binding domains. Thus, they are commonly referred to as ATP-independent chaperone proteases. Whereas the function of ATP-dependent chaperone-proteases is regulated by ATP hydrolysis, HtrA exhibits a PDZ domain and a temperature-dependent switch mechanism, which effects the change in its function from molecular chaperone to protease. This mechanism is also related to substrate recognition and the fine control of its function. Structural and biochemical analyses of the three HtrA proteins, DegP, DegQ, and DegS, have provided us with clues as to the functional regulation of HtrA proteins, as well as their roles in protein quality control at atomic scales. The objective of this brief review is to discuss some of the recent studies which have been conducted regarding the structure and function of these HtrA proteins, and to compare their roles in the context of protein quality control.

• Biomolecules & Therapeutics
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• v.31 no.2
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• pp.141-147
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• 2023

Antibiotic resistance has emerged as a global threat to modern healthcare systems and has nullified many commonly used antibiotics. β-Lactam antibiotics are among the most successful and occupy approximately two-thirds of the prescription antibiotic market. They inhibit the synthesis of the peptidoglycan layer in the bacterial cell wall by mimicking the D-Ala-D-Ala in the pentapeptide crosslinking neighboring glycan chains. To date, various β-lactam antibiotics have been developed to increase the spectrum of activity and evade drug resistance. This review emphasizes the three-dimensional structural characteristics of β-lactam antibiotics regarding the overall scaffold, working mechanism, chemical diversity, and hydrolysis mechanism by β-lactamases. The structural insight into various β-lactams will provide an in-depth understanding of the antibacterial efficacy and susceptibility to drug resistance in multidrug-resistant bacteria and help to develop better β-lactam antibiotics and inhibitors.

• Journal of Animal Science and Technology
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• v.65 no.6
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• pp.1151-1168
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• 2023

Tenderness and taste characteristics of meat are the key determinants of the meat choices of consumers. This review summarizes the contemporary research on the molecular mechanisms by which postmortem aging of meat improves the tenderness and taste characteristics. The fundamental mechanism by which postmortem aging improves the tenderness of meat involves the operation of the calpain system due to apoptosis, resulting in proteolytic enzyme-induced degradation of cytoskeletal myofibrillar proteins. The improvement of taste characteristics by postmortem aging is mainly explained by the increase in the content of taste-related peptides, free amino acids, and nucleotides produced by increased hydrolysis activity. This review improves our understanding of the published research on tenderness and taste characteristics of meat and provides insights to improve these attributes of meat through postmortem aging.