• Clean Technology
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• v.20 no.2
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• pp.130-135
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• 2014

It is investigated that the surface properties of mercaptopyruvic-acid layer formed on gold surfaces may make an effect on the distribution of either gold particle adsorbed to the zirconia surface or vice versa. For the investigation, the atomic force microscope was used to measure the surface forces between the surfaces as a function of the salt concentration and pH value. The forces were quantitatively analyzed with the derjaguin-landau-verwey-overbeek (DLVO) theory to estimate the electrostatic properties, potential and charge density, of the surfaces for each condition of salt concentration and pH value. The estimatedvalue dependence on the salt concentration was explained with the law of mass action, and the pH dependence was interpreted with the ionizable groups on the surface. The salt concentration dependence of the surface properties, found from the measurement at pH 4 and 8, was predictable from the law. It was found that the mercaptopyruvic-acid layer had higher values for the surface charge densities and potentials than the zirconia surfaces at pH 4 and 8, which may be attributed to the ionizedfunctional-groups of the mercaptopyruvic-acid layer.

• Bulletin of the Korean Chemical Society
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• v.24 no.5
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• pp.627-632
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• 2003

The pH dependence of the kinetic parameters of recombinant acetohydroxy acid synthase catalyzed reaction was determined in order to obtain information about the chemical mechanism, particularly acid-base chemistry. The maximum velocity and V/K for pyruvate were bell-shaped with estimated pK values of 6.5-6.7 and 8.6-8.9, respectively. The maximum velocity and V/K for 2-ketobutyrate were also bell-shaped with estimated pK values of 6.6-7.0 and 8.4-8.6. The pH dependence of 1/Ki for 3-bromopyruvate, a competitive inhibitor of pyruvate, was also bell-shaped, giving pK values almost identical with those obtained for pyruvate. Since the same pK values were observed in the $pK_{i 3-bromopyruvate}$, V/K pH profiles and $V_{max}$ profiles, both enzyme groups must be in their optimum protonation state for efficient binding of reactants. These results reflect that two enzyme groups are necessary for binding of substrate and/or catalysis.

• BMB Reports
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• v.28 no.3
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• pp.204-209
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• 1995

The pH dependence of kinetic parameters in the amination direction of the aspartase from Hafnia alvei has been determined. The V/K for fumarate is bell shaped with pK values of 6.4 and 8.7. The maximum velocity for fumarate is also bell shaped with pK values of 7.2 and 9.1. The pH dependence of 1/K, for potassium (competitive inhibitor of ammonia) decreases at low pH with pK 7.6. Together with data [Yoon and Cook (1994) Korean J. Biochem. 27, 1-5] on the deamination direction of the aspartase, these results are consistent with two enzyme groups which are necessary for catalysis. An enzymatic group that must be deprotonated has been identified. Another enzyme group must be protonated for substrate binding. Both the general base and general acid group are in a protonation state opposite that in which they started when aspartate was bound. A proton is abstracted from C-3 of the monoanionic form of L-aspartate by an enzyme general base with, a pK of 6.3~6.6 in the absence and presence of $Mg^{2+}$ Ammonia is then expelled with the assistance of a general acid group giving $NH_{4+}$ as the product.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1479-1484
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• 2010

Photosynthesis uses light energy to drive the oxidation of water at an oxygen-evolving catalytic site within photosystem II (PSII). Chlorophyll binding by the photosystem II subunit S protein, PsbS, was found to be necessary for energy-dependent quenching (qE), the major energy-dependent component of non-photochemical quenching (NPQ) in Arabidopsis thaliana. It is proposed that PsbS acts as a trigger of the conformational change that leads to the establishment of nonphotochemical quenching. However, the exact structure and function of PsbS in PSII are still unknown. Here, we clone and express the recombinant PsbS gene from Arabidopsis thaliana in E. coli and purify the resulting homogeneous protein. We used various biochemical and biophysical techniques to elucidate PsbS structure and function, including circular dichroism (CD), fluorescence, and DSC. The protein shows optimal stability at $4^{\circ}C$ and pH 7.5. The CD spectra of PsbS show that the conformational changes of the protein were strongly dependent on pH conditions. The CD curve for PsbS at pH 10.5 curve had the deepest negative peak and the peak of PsbS at pH 4.5 was the least negative. The fluorescence emission spectrum of the purified PsbS protein was also measured, and the ${\lambda}_{max}$ was found to be at 328 nm. PsbS revealed some structural changes under varying temperature and oxygen gas condition.

• YAKHAK HOEJI
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• v.34 no.5
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• pp.302-310
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• 1990

A study has been made of the Korean bentonite aqueous suspension contrast with American bentonite by means of XRD IR swelling, gel formation and rheogram at various conditions such as concentration, temperature and pH. The Korean bentonite was identified as montmorillonite clay containig a small proprotion of crystoballite and mordenite, and its swelling power were acceptable for requirements of Korean pharmacopeia regulations though its values were not satisfied. Korean bentonite swelled to 10 times and American one did to 15 times compared to its bulkiness of powder. The rheogram of Korean bentonite suspension reveals bulged pseudoplatic flow with yield value at higher concentration and pseudoplastic flow without yield value at lower concentration. The higher the concentration, the greater were the apparent viscosity and hysteresis loop. Korean bentonite suspension showed insignificant temperature dependence on both apparent viscosity and hysteresis loop and it was more temperature dependent on viscosity but less on hysteresis loop than those of American sample. The pH dependence was so high on viscosity that apparent minimum value was near pH 7 and maximum value at pH 3 or 7. The hysteresis loop appeared minimum over the pH range 5-7 and maximum near pH 3 or 11. The Korean bentonite was inferior to the American bentonite in swelling volume, gel formation, thioxotropy, however, it would be possible to improve the quality of Korean bentonite by developing the method of purification for bentonite clay.

• Food Science of Animal Resources
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• v.29 no.3
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• pp.325-333
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• 2009

Beef quality indicators of off-flavor development during storage were investigated in terms of temperature dependence. The off-flavor development time (ODT) was detected using the R-index sensory test. During varying storage conditions at $25^{\circ}C$, $15^{\circ}C$, and $5^{\circ}C$, elements of beef quality were measured, such as volatile basic nitrogen (VBN), pH, color (CIE $L^*$, $a^*$, $b^*$), Warner-Bratzler shear force (WBSF), Pseudomonas spp. CFU, and lactic acid bacteria (LAB) CFU. A model with temperature dependence of ODT during storage was developed using Arrhenius-like equation, and a requirement with quality indicators was mathematically derived, resulting in similar temperature dependence. The temperature dependence of beef quality indicators was represented by the Arrhenius activation energy (Ea). Upon comparing the Ea of beef quality indicators and ODT, the temperature dependence similarity was found to be higher in the order of three groups: VBN, pH, $a^*$ value; LAB, Pseudomonas spp.; and WBSF, $L^*$ value, $b^*$ value. Therefore, VBN were determined as the most effective indicator of beef quality during off-flavor development.

• Fisheries and Aquatic Sciences
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• v.3 no.3_4
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• pp.188-194
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• 2000

A protease purified from hepatopancreas of shrimp, Penaeus japonicus, had maximum activity at $70^{\circ}C$ and in neutral and alkaline pH ranges. Specific activity at optimum reaction condition of the protease was estimated to be approximately 12 U/mg/min. The protease was stable in neutral and alkaline pH ranges and activity was retained after heat treatment at $50^{\circ}C$ for 30 min. Apparent $K_m$ and $V_{max}$ value against casein substrate were estimated to be $0.29\%$ and $7.8see^{-1}$, respectively, and those against N-CBZ-L-tyrosine p-nitropheny1 ester (CBZ­Tyr-NE) were 0.38 mM and $2,400 see^{-1}$, respectively. The N-termina1 sequence of the protease showed high homology to the trypsin from same species and the proteases from shrimp. Myosin heavy chain (MHC) from shrimp tail meat was the most susceptible to the protease and actin/tropomyosin were degraded progressively during 4 hr incubation, but to a lesser degree than MHC.

• The Korean Journal of Physiology
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• v.11 no.2
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• pp.1-7
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• 1977

The activity of the $Ca^{++}$ activated adenosinetriphosphatase (Ca-ATPase) of actomyosin systeme of rabbit and frog skeletal muscle has been studied at varying pH and temperature. The PH optima of the Ca-ATPase activity of the rabbit actomyosin was rather broad. Over the temperature range of $16-36^{\circ}C$ activity of the enzyme was not appreciably changed between pH 6.4-8.5; below and above which it rapidly reduced. The pH at the inflection point of the enzyme activity increased as temperature decreased, showing the ${\bigtriangleup}pH\;inflection/{\bigtriangleup}T$ of approximately $-0.018\;unit/^{\circ}C$. Consequently, $(OH^-)/(H^+)$ ratio at the inflection point was constant regardless of assay temperature. In the frog actomyosin systems the Ca-ATPase activity was not apparently altered between PH 6.4-7.0 when the incubation temperature was $15{\sim}30^{\circ}C$. Outside of this range of pH, however, the enzyme activity was dramatically decreased. The pH of the inflection point changed inversely with temperature. ${\bigtriangleup}pH\;inflection/{\bigtriangleup}T$ at the acidic side was approximately $-0.018\;unit/^{\circ}C$, whereas that at the alkaline side it was about $-0.037\;unit/^{\circ}C$. The Arrhenius Plot on the Ca-ATPase activity at constant $(OH^-)/(H^+)$ ratio of 1.0 was not linear, but showed break at arround $20^{\circ}C$ for both rabbit and frog actomyosin Preparations. From these results it was speculated that pH dependence of Ca-ATPase activity of rabbit actomyosin systems might reflect titrations of histidine-imidazole and -SH groups, and that of the frog actomyosin represents titrations of histidine-imidazole and lysyllysine ${\alpha}-NH_2$ groups.

• Bulletin of the Korean Chemical Society
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• v.31 no.7
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• pp.1920-1926
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• 2010

Yoon et $al.^1$ presented an approximate mathmatical model to describe ammonia removal from an experimental batch reactor system with gaseous headspace. The development of the model was initially based on assuming instantaneous equilibrium between ammonia in the aqueous and gas phases. In the model, a "saturation factor, $\beta$" was defined as a constant and used to check whether the equilibrium assumption was appropriate. The authors used the trends established by the estimated $\beta$ values to conclude that the equilibrium assumption was not valid. The authors presented valuable experimental results obtained using a carefully designed system and the model used to analyze the results accounted for the following effects: speciation of ammonia between $NH_3$ and $NH^+_4$ as a function of pH; temperature dependence of the reactions constants; and air flow rate. In this article, an alternative model based on the exact solution of the governing mass-balance differential equations was developed and used to describe ammonia removal without relying on the use of the saturation factor. The modified model was also extended to mathematically describe the pH dependence of the ammonia removal rate, in addition to accounting for the speciation of ammonia, temperature dependence of reactions constants, and air flow rate. The modified model was used to extend the analysis of the original experimental data presented by Yoon et $al.^1$ and the results matched the theory in an excellent manner.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.2855-2860
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• 2012

The coating N-acetyl cysteine (NAC) on gold surfaces may be used to design the distribution of either gold particle adsorbed to the $ZrO_2$ surface or vice versa by adjusting the electrostatic interactions. In this study, it was performed to find out electrostatic properties of the NAC-coated-gold surface and the $ZrO_2$ surface. The surface forces between the surfaces were measured as a function of the salt concentration and pH value using the AFM. By applying the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to the surface forces, the surface potential and charge density of the surfaces were quantitatively acquired for each salt concentration and each pH value. The dependence of the potential and charge density on the concentration was explained with the law of mass action, and the pH dependence was with the ionizable groups on the surface.