排序方式: 共有107条查询结果,搜索用时 31 毫秒
11.
Choi KW Park KM Jun SY Park CS Park KH Cha J 《Journal of microbiology and biotechnology》2008,18(5):901-907
Thermotoga neapolitana beta-glucosidase (BglA) was subjected to site-directed mutagenesis in an effort to increase its ability to synthesize arbutin derivatives by transglycosylation. The transglycosylation reaction of the wild-type enzyme displays major beta(1,6) and minor beta(1,3) or beta(1,4) regioselectivity. The three mutants, N291T, F412S, and N291T/F412S, increased the ratio of transglycosylation/hydrolysis compared with the wild-type enzyme when pNPG and arbutin were used as a substrate and an acceptor, respectively. N291T and N219T/F412s had transglycosylation/hydrolysis ratios about 3- and 8-fold higher, respectively, than that of the wild-type enzyme. This is due to the decreased hydrolytic activity of the mutant rather than increased transglycosylation activity. Interestingly, N291T showed altered regioselectivity, as well as increased transglycosylation products. TLC analysis of the transglycosylation products indicated that N291T retained its beta(1,3) regioselectivity, but lost its beta(1,4) and beta(1,6) regioselectivity. The altered regioselectivity of N291T using two other acceptors, esculin and salicin, was also confirmed by TLC. The major transglycosylation products of the wild type and N291T mutant were clearly different. This result suggests that Asn-291 is highly involved in the catalytic mechanism by controlling the transglycosylation reaction. 相似文献
12.
Kang HK Cha H Yang TJ Park JT Lee S Kim YW Auh JH Okada Y Kim JW Cha J Kim CH Park KH 《Biochemical and biophysical research communications》2008,366(1):98-103
Di-O-α-maltosyl-β-cyclodextrin ((G2)2-β-CD) was synthesized from 6-O-α-maltosyl-β-cyclodextrin (G2-β-CD) via a transglycosylation reaction catalyzed by TreX, a debranching enzyme from Sulfolobus solfataricus P2. TreX showed no activity toward glucosyl-β-CD, but a transfer product (1) was detected when the enzyme was incubated with maltosyl-β-CD, indicating specificity for a branched glucosyl chain bigger than DP2. Analysis of the structure of the transfer product (1) using MALDI-TOF/MS and isoamylase or glucoamylase treatment revealed it to be dimaltosyl-β-CD, suggesting that TreX transferred the maltosyl residue of a G2-β-CD to another molecule of G2-β-CD by forming an α-1,6-glucosidic linkage. When [14C]-maltose and maltosyl-β-CD were reacted with the enzyme, the radiogram showed no labeled dimaltosyl-β-CD; no condensation product between the two substrates was detected, indicating that the synthesis of dimaltosyl-β-CD occurred exclusively via transglycosylation of an α-1,6-glucosidic linkage. Based on the HPLC elution profile, the transfer product (1) was identified to be isomers of 61,63- and 61,64-dimaltosyl-β-CD. Inhibition studies with β-CD on the transglycosylation activity revealed that β-CD was a mixed-type inhibitor, with a Ki value of 55.6 μmol/mL. Thus, dimaltosyl-β-CD can be more efficiently synthesized by a transglycosylation reaction with TreX in the absence of β-CD. Our findings suggest that the high yield of (G2)2-β-CD from G2-β-CD was based on both the transglycosylation action mode and elimination of the inhibitory effect of β-CD. 相似文献
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14.
Cho HK Kim HH Seo DH Jung JH Park JH Baek NI Kim MJ Yoo SH Cha J Kim YR Park CS 《Enzyme and microbial technology》2011,49(2):246-253
Amylosucrase (ASase, EC 2.4.1.4) is a glucosyltransferase that hydrolyzes sucrose into glucose and fructose and produces amylose-like glucan polymers from the released glucose. (+)-Catechin is a plant polyphenolic metabolite having skin-whitening and antioxidant activities. In this study, the ASase gene from Deinococcus geothermalis (dgas) was expressed in Escherichia coli, while the recombinant DGAS enzyme was purified using a glutathione S-transferase fusion system. The (+)-catechin glycoside derivatives were synthesized from (+)-catechin using DGAS transglycosylation activity. We confirmed the presence of two major transglycosylation products using TLC. The (+)-catechin transglycosylation products were isolated using silica gel open column chromatography and recycling-HPLC. Two (+)-catechin major transfer products were determined through 1H and 13C NMR to be (+)-catechin-3′-O-α-d-glucopyranoside with a glucose molecule linked to (+)-catechin and (+)-catechin-3′-O-α-D-maltoside with a maltose linked to (+)-catechin. The presence of (+)-catechin maltooligosaccharides in the DGAS reaction was also confirmed via recycling-HPLC and enzymatic analysis. The effects of various reaction conditions (temperature, enzyme concentration, and molar ratio of acceptor and donor) on the yield and type of (+)-catechin glycosides were investigated. 相似文献
15.
Molecular cloning and biochemical characterization of a heat-stable type I pullulanase from Thermotoga neapolitana 总被引:1,自引:0,他引:1
Kang J Park KM Choi KH Park CS Kim GE Kim D Cha J 《Enzyme and microbial technology》2011,48(3):260-266
The gene encoding a type I pullulanase from the hyperthermophilic anaerobic bacterium Thermotoga neapolitana (pulA) was cloned in Escherichia coli and sequenced. The pulA gene from T. neapolitana showed 91.5% pairwise amino acid identity with pulA from Thermotoga maritima and contained the four regions conserved in all amylolytic enzymes. pulA encodes a protein of 843 amino acids with a 19-residue signal peptide. The pulA gene was subcloned and overexpressed in E. coli under the control of the T7 promoter. The purified recombinant enzyme (rPulA) produced a 93-kDa protein with pullulanase activity. rPulA was optimally active at pH 5-7 and 80°C and had a half-life of 88 min at 80°C. rPulA hydrolyzed pullulan, producing maltotriose, and hydrolytic activities were also detected with amylopectin, starch, and glycogen, but not with amylose. This substrate specificity is typical of a type I pullulanase. Thin layer chromatography of the reaction products in the reaction with pullulan and aesculin showed that the enzyme had transglycosylation activity. Analysis of the transfer product using NMR and isoamylase treatment revealed it to be α-maltotriosyl-(1,6)-aesculin, suggesting that the enzyme transferred the maltotriosyl residue of pullulan to aesculin by forming α-1,6-glucosidic linkages. Our findings suggest that the pullulanase from T. neapolitana is the first thermostable type I pullulanase which has α-1,6-transferring activity. 相似文献
16.
Suppression of Inducible Nitric Oxide Synthase Expression by Nyasol and Broussonin A,Two Phenolic Compounds from Anemarrhena asphodeloides,through NF‐κB Transcriptional Regulation in vitro and in vivo 下载免费PDF全文
Eun Jin Lee Hwa‐Jin Chung Yuna Pyee Ji‐Young Hong Ui Joung Youn Eun‐Kyoung Seo Sang Kook Lee 《化学与生物多样性》2014,11(5):749-759
17.
Simultaneously Enhancing Light Extraction and Device Stability of Organic Light‐Emitting Diodes using a Corrugated Polymer Nanosphere Templated PEDOT:PSS Layer 下载免费PDF全文
18.
Superlattice Formation of Crystal Water in Layered Double Hydroxides for Long‐Term and Fast Operation of Aqueous Rechargeable Batteries 下载免费PDF全文
Ji Hoon Lee Hyeon Jeong Lee Sun Hee Choi Jaeho Shin Sung‐Yoon Chung Jang Wook Choi 《Liver Transplantation》2018,8(18)
Aqueous rechargeable batteries (ARBs) are gaining increasing attention as alternatives to conventional nonaqueous lithium ion batteries. However, finding electrode materials with competitive electrochemical properties in various aspects is challenging. Moreover, the operation mechanism of some of high performance electrode materials is not fully understood. Here, an α‐phase layered double hydroxide (α‐LDH) working in alkaline electrolytes as an ARB cathode is reported. On charge, OH? carrier ions intercalate into the interlayer space and react with protons detached from the host structure to yield crystal water. This crystal water is then arranged in a superlattice during charging to accommodate carrier ions and stabilize the structure. The solid solution mixing of cobalt and nickel also stabilizes the structure during the wide range of redox swing of Ni from 2+ to 4+. In pairing with Fe3O4/Fe(OH)2 mixture, the α‐LDH exhibits 198.0 mA h g?1 at 3 A g?1, 68.3% capacity retention after 10 000 cycles, and 172.5 mA h g?1 at 1 min charge, demonstrating the promise of hydrated compounds for ARB electrodes. The present study elucidates that the arrangement of crystal water within the host framework plays a critical role in determining the electrochemical performance of the corresponding hydrated active compound in aqueous media. 相似文献
19.
Yeona Cho Jee Suk Chang Koon Ho Rha Sung Joon Hong Young Deuk Choi Won Sik Ham Jun Won Kim Jaeho Cho 《PloS one》2016,11(1)
Purpose/Objectives
Treatment of the primary tumor reportedly improves survival in several types of metastatic cancer. We herein evaluated the efficacy and toxicity of radiotherapy for the primary tumor in prostate cancer with metastasis.Materials/Methods
The study cohort included 140 men with metastatic prostate cancer at initial diagnosis. Metastatic sites were divided into 4 groups as follows: solitary bone, 2–4 bones, ≥5 bones, and visceral organs. Patient, tumor, and treatment characteristics, and clinical outcomes were compared between patients treated with (prostate radiotherapy [PRT] group) or without radiotherapy to the primary tumor.Results
Patients in PRT group presented with a statistically significantly younger age (p = .02), whereas other characteristics showed no significant difference. Overall survival (OS) and biochemical failure-free survival (BCFFS) were improved in PRT patients (3-year OS: 69% vs. 43%, p = 0.004; 3-year BCFFS: 52% vs. 16%, p = 0.002). Multivariate analysis identified PRT as a significant predictor of both OS (hazard ratio [HR] = 0.43, p = 0.015). None of the 38 PRT patients experienced severe (grade ≥3) genitourinary or gastrointestinal toxicity.Conclusions
Our data suggest that radiotherapy to the primary tumor was associated with improved OS and BCFFS in metastatic prostate cancer. The results of this study warrant prospective controlled clinical trials of this approach in stage IV prostate cancer patients with limited extent of bone metastasis and good performance status. 相似文献20.
Kim YM Seo J Kim YH Jeong J Joo HJ Lee DH Koh GY Lee KJ 《Journal of proteome research》2007,6(8):3278-3290
Angiogenesis is an essential process in physiological and pathological processes and is well-regulated to maintain the cellular homeostasis by balancing the endothelial cells in proliferation and apoptosis. Angiopoietin-1 (Ang1) regulates angiogenesis as a ligand of Tie 2 receptor tyrosine kinase. However, the regulation pathways are not well-understood. To date, only a few of the signaling molecules involved in the Tie 2 receptor tyrosine kinase-mediated angiogenesis have been identified. In this study, we systematically identified tyrosine-phosphorylated proteins in Ang1-induced signaling cascade in human umbilical vein endothelial cells (HUVECs), employing proteomic analyses combining two-dimensional gel electrophoresis, Western analysis using phosphotyrosine antibody and mass spectrometry (MALDI-TOF MS and nanoLC-ESI-q-TOF tandem MS). We report here the identification, semiquantitative analysis, and kinetic changes of tyrosine-phosphorylated proteins in response to Ang1 in HUVECs and identified 66 proteins among 69 protein spots showing significant changes. Of these, p54nrb was validated as a molecule involved in cell migration. These results suggest that Ang1 induces stabilization of neo-vessel network by regulating the phosphorylations of metabolic and structural proteins. 相似文献