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Choi, B.Y.,Yun, S.T.,Kim, K.H.,Choi, H.S.,Chae, G.T.,Lee, P.K. Elsevier 2014 Journal of geochemical exploration Vol.144 No.1
Naturally outflowing CO<SUB>2</SUB>-rich springs are a natural analogue of the seepage of sequestered CO<SUB>2</SUB> in geological storage sites. In Kangwon district of South Korea, two hydrochemically different types of CO<SUB>2</SUB>-rich springs (i.e., Ca-HCO<SUB>3</SUB>-type and Na-HCO<SUB>3</SUB>-type) occur together in a granitic terrain. Hydrochemical and water-isotope data (i.e., δ<SUP>18</SUP>O-δD and tritium) show that Na-HCO<SUB>3</SUB>-type springs have experienced significant silicate weathering processes over a long residence time at depths, while Ca-HCO<SUB>3</SUB>-type springs were formed by the mixing of Na-HCO<SUB>3</SUB>-type springs with shallow groundwater during ascent. In this study, diverse geochemical models including mixing, ion exchange and reaction path were investigated to verify the geochemical processes accounting for the occurrence of two contrasting types of CO<SUB>2</SUB>-rich springs. The mixing and ion exchange models reveal that Ca-HCO<SUB>3</SUB>-type springs are well explained by reverse cation exchange occurring during the mixing of Na-HCO<SUB>3</SUB>-type springs with shallow groundwater. The Na-HCO<SUB>3</SUB>-type springs are well explained by the reaction path modeling including the dissolution of silicate minerals (plagioclase, K-feldspar and biotite) and the precipitation of secondary minerals (calcite, kaolinite, muscovite and Mg-beidellite), implying that dissolved carbon is sequestered by calcite precipitation (i.e., mineral trapping). However, the concentrations of K in our modeling results are far below those of K observed in Na-HCO<SUB>3</SUB>-type springs, because of the precipitation of muscovite considered in the model, suggesting the partial disequilibrium state of the aquifer during the hydrolysis of K-feldspar under high P<SUB>CO'2</SUB> conditions. This result implies that to better predict long-term CO<SUB>2</SUB>-water-rock interactions in a geological storage site with abundant K-feldspar, the secondary K-bearing minerals should be carefully predicted, because a target aquifer can be far from chemical equilibrium during the storage period. This study shows that geochemical modeling can be effectively used to predict the hydrochemical changes of groundwater during long-term CO<SUB>2</SUB>-water-rock interactions and subsequent leakage toward surface in K-feldspar rich aquifer, although it should be included in a fully coupled computational approach between fluid flow, heat transfer and reactive mass transport processes in the future research.
Nguyen, N.T.T.,Lee, J.S.,Yun, S.,Lee, E.K. Elsevier 2016 Journal of Chromatography A Vol.1457 No.-
<P>Exenatide is a synthetic version of the 39-mer peptide of Exendin-4, which is an FDA-approved therapeutic against Type II diabetes mellitus. However, exenatide has a very short in-serum half-life and PEGylation have been performed to improve its in-serum stability. PEGylation often yields multivalent binding to non-specific residues, and the desired species should be carefully separated by chromatographies. In this study, we first devised an aqueous-phase, two-step PEGylation process. This consists of thiolation of Lys 12 and 27 residues followed by attachment of PEG-maleimide (10 kD) to thiol groups. This process yields various species: mono-PEGylates with positional isomers, di-PEGylate, and other higher MW substances. A prep-grade cationic exchange chromatography (HiTrap SP) at pH 3.0 partially separated mono- and di-PEGylates based on the molar ratio of conjugated PEG and peptide and thus molecular weight of the conjugates. To further investigate the chromatographic separation of positional isomers of mono-PEGylates, we prepared two kinds of exenatide analogs by point mutation; K12C and K27C. Each analog was mono-PEGylated with very high yield (>95%). When a mixture of the two positional isomers of mono-PEGylates was applied to HiTrap SP chromatography, K12C-PEGylate and K27C-PEGylate eluted separately at 0.22 M and 0.33 M NaCl, respectively. When the proportions of acid and its conjugate base of the amino acid residues adjacent to the PEGylation site at pH 3.0 were analyzed, K27C-PEGylate shows stronger positive charge than K12C-PEGylate, and we propose the residence time difference between the two mono-PEGylates could be due to the charge difference. ELISA result shows that the immuno-binding activity of both analogs and their mono-PEGylates are well maintained. Furthermore, both mono-PEGylates of the analogs show higher than 50-fold improved anti-trypsin stability. We expect that mono-PEGylates of the exenatide analogs are alternatives to the conventional C40-PEG. (C) 2016 Elsevier B.V. All rights reserved.</P>
Role of conserved Met112 residue in the catalytic activity and stability of ketosteroid isomerase
Cha, H.J.,Jang, D.S.,Jeong, J.H.,Hong, B.H.,Yun, Y.S.,Shin, E.J.,Choi, K.Y. Elsevier Science 2016 Biochimica et biophysica acta. Proteins and proteo Vol.1864 No.10
<P>Ketosteroid isomerase (3-oxosteroid Delta(5)-Delta(4)-isomerase, KSI) from Pseudomonas putida catalyzes allylic rearrangement of the 5,6-double bond of Delta(5)-3-ketosteroid to 4,5-position by stereospecific intramolecular transfer of a proton. The active site of KSI is formed by several hydrophobic residues and three catalytic residues (Tyr14, Asp38, and Asp99). In this study, we investigated the role of a hydrophobic Met112 residue near the active site in the catalysis, steroid binding, and stability of KSI. Replacing Met112 with alanine (yields M112A) or leucine (M112L) decreased the k(cat) by 20- and 4-fold, respectively. Compared with the wild type (WT), M112A and M112L KSIs showed increased K-D values for equilenin, an intermediate analogue; these changes suggest that loss of packing at position 112 might lead to unfavorable steroid binding, thereby resulting in decreased catalytic activity. Furthermore, M112A and M112L mutations reduced melting temperature (T-m) by 6.4 degrees C and 2.5 degrees C, respectively. These changes suggest that favorable packing in the core is important for the maintenance of stability in KSI. The M112K mutation decreased k(cat) by 2000-fold, compared with the WT. In M112K KSI structure, a new salt bridge was formed between Asp38 and Lys112. This bridge could change the electrostatic potential of Asp38, and thereby contribute to the decreased catalytic activity. The M112K mutation also decreased the stability by reducing T-m by 4.1 degrees C. Our data suggest that the Met112 residue may contribute to the catalytic activity and stability of KSI by providing favorable hydrophobic environments and compact packing in the catalytic core. (C) 2016 Published by Elsevier B.V.</P>
Yun, J.Y.,Park, K.S.,Kim, J.H.,Do, S.H.,Zuo, Z. North-Holland 2007 European journal of pharmacology Vol.565 No.1-3
The authors investigated the effects of propofol on EAAT3 (excitatory amino acid transporter 3) activity under oxidative stress induced by tert-butyl hydroperoxide (t-BHP), and the mediation of these effects by protein kinase C (PKC). Rat EAAT3 was expressed in Xenopus oocytes and L-glutamate (30 μM)-induced membrane currents were measured using the two-electrode voltage clamp technique. Exposure of these oocytes to t-BHP (1-20 mM) for 10 min dose-dependently decreased EAAT3 activity, and t-BHP (5 mM) significantly decreased the V<SUB>max</SUB>, but not the K<SUB>m</SUB> of EAAT3 for glutamate, and propofol (1-100 μM) dose-dependently reversed this t-BHP-attenuated EAAT3 activity. Phorbol-12-myristate-13-acetate (a PKC activator), also abolished this t-BHP-induced reduction in EAAT3 activity, whereas staurosporine (a PKC inhibitor), significantly decreased EAAT3 activity. However, as compared with staurosporine or t-BHP alone, t-BHP and staurosporine in combination did not further reduce EAAT3 activity. A similar pattern was observed for chelerythrine (also a PKC inhibitor). In oocytes pretreated with combinations of t-BHP and PMA (or staurosporine), propofol failed to change EAAT3 activity. Our results suggest that propofol restores oxidative stress-reduced EAAT3 activity and that these effects of propofol may be PKC-mediated.
Yun, S.,Ryu, H.,Lee, E.K. Elsevier Science Publishers 2017 Journal of biotechnology Vol.257 No.-
<P>Phage display biopanning is a powerful in vitro selection process for screening and identifying peptides that bind to a target protein of interest. With the aim of replacing antibodies in immuno-diagnostic applications, we identified peptides whose binding characteristics mimicked those of anti-human myeloperoxidase (hMPO), a biomarker for acute cardiac diseases. Based on ELISA results from four phage clones, we selected and chemically synthesized a 12-mer peptide (SYIEPPERHRHR). Quartz crystal microbalance and surface plasmon resonance analyses revealed that the molar binding equilibrium ratio of the synthesized peptide was 0.023, approximately 43-fold lower than that of the anti-hMPO antibody. The dissociation constant (K-d) was 57 nM, which was comparable to that of the native antibody (83 nM). Next, we biotinylated the peptide at its N-terminus and attached the biotinylated peptide to the surface of streptavidin-coated magnetic particles to assess its ability to selectively capture hMPO. The binding equilibrium data were similar to the previous analyses; specifically, around 0.021 mol peptide bound to 1 mol of hMPO. Antigen capture was found to be selective and to be relatively little influenced by the presence of human serum albumin (HSA), an abundant constituent of serum. Our work demonstrates the potential of immunomagnetic isolation to achieve selective capture of a low-concentration antigen from complex solutions such as serum. (C) 2016 Elsevier B.V. All rights reserved.</P>