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Poly-l-lysine can form either of three different conformers as α-helix, anti-parallel β-sheet and random coil stably under appropriate conditions. In buffer solution poly-l-lysine exists in a random coil at about pH 4, an α-helix above pH 12, and transforms from α-helix to β-sheet when the sample is heated to 46 °C for 30 min. The effects of elevated hydrostatic pressure on three different initial conformers of poly-l-lysine are investigated with Fourier transform infrared spectroscopy and two-dimensional correlation analysis. Changes observed in the amide I′ band indicate that the α-helix conformer undergo hydration enhancement at low pressure (<400 MPa), then gradually transition into an α′-helix. Two initial conformers, the β-sheet and random coiled polypeptide, undergo conformational changes to an α-helix at low pressure and to an α′-helix at high pressure. Moreover, the conversion occurred at a lower pressure for the β-sheet (∼250 MPa) than for the α-helix (∼300 MPa) and the random coil (∼850 MPa). 相似文献
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Xiao H Xie Y Liu Q Xu X Shi C 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(13-14):2840-2848
A novel copper-containing enzyme named COI (catechol oxidase I) has been isolated and purified from tobacco by extracting acetone-emerged powder with phosphate buffer, centrifugation at low temperature, ammonium sulfate fractional precipitation, and column chromatography on DEAE-sephadex (A-50), sephadex (G-75), and DEAE-celluse (DE-52). PAGE, SDS-PAGE were used to detect the enzyme purity, and to determine its molecular weight. Then the secondary structures of COI at different pH, different temperatures and different concentrations of guanidine hydrochloride (GdnHCl) were studied by the FT-IR, Fourier self-deconvolution spectra, and circular dichroism (CD). At pH 2.0, the contents of both alpha-helix and anti-parallel beta-sheet decrease, and that of random coil increases, while beta-turn is unchanged compared with the neutral condition (pH 7.0). At pH 11.0, the results indicate that the contents of alpha-helix, anti-parallel beta-sheet and beta-turn decrease, while random coil structure increases. According to the CD measurements, the relative average fractions of alpha-helix, anti-parallel beta-sheet, beta-turn/parallel beta-sheet, aromatic residues and disulfide bond, and random coil/gamma-turn are 41.7%, 16.7%, 23.5%, 11.3%, and 6.8% at pH 7.0, respectively, while 7.2%, 7.7%, 15.2%, 10.7%, 59.2% at pH 2.0, and 20.6%, 9.5%, 15.2%, 10.5%, 44.2% at pH 11.0. Both alpha-helix and random coil decrease with temperature increasing, and anti-parallel beta-sheet increases at the same time. After incubated in 6 mol/L guanidine hydrochloride for 30 min, the fraction of alpha-helix almost disappears (only 1.1% left), while random coil/gamma-turn increases to 81.8%, which coincides well with the results obtained through enzymatic activity experiment. 相似文献
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In order to investigate the interaction between exogenous Cu2+ and Polyphenoloxidase (PPO) from Nictiana Tobacum, the Cu2+-induced resistant-denaturation against guanidine hydrochloride(Gdn-HCl) was studied by the following enzymatic activity assay, fluorescence spectroscopy and circular dichroism (CD). The results show that the GdnHCl-induced unfolding is a two-state process with no detectable inter mediate state in the absence of exogenous Cu2+, while the GdnHCl-induced unfolding in the presence of 10.0 mmol/L exogenous Cu2+ follows a three-state transition with an intermediate state, which results from the fact that Cu2+ increases the structural stability of native PPO and its intermediate. In terms of enzymatic activities, 6 mol/L GdnHCl makes PPO lose 81.4% of its original activity after 5 min, inactivate completely after 30 min, while in the presence of 10.0 mmol/L exogenous Cu2+, only 39.4% and 75.1%, after 5 and 30 min respectively. According to the CD measurements, the relative average fractions of α-helix, anti-parallel2-sheet, 2-turn/parallel 2-sheet, aromatic residues and disulfide bond, and random coil/γ-turn are 1.1%, 3.8%, 3.3%, 7.5% and 84.3%, respectively, in the 6.0mol/L GdnHCl containing no CuSO4, but34.2%, 13.7%, 21.0%, 9.5% and 21.6%, respectively, in the same concentration of Gdn-HCl containing 10mmol/L CuSO4. 相似文献
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1INTRODUCTIONTheplanttoxin,CrotinIisoneoftheribosomeinactivatingproteins(RIPs)[l3.AccordingtothemolecularmechanismofactiontheRIPscanbedividedintotwokinds[2:.OnebelongstoRNAN-glycosidasewhichisclassifiedastwotypes.TypeIconsistsofasinglepolypeptidechain,forexample,trichosanthinandsaporin-Typellconsistsoftwochains,suchasricinandabrin'ThiskindofRIPshydrolysesasingleN-glycosidicbondbetweenanadenineandriboseatspecificnu-cleotide(A4324)of28SrRNAintheribosomes[3i.ThesecondkindofRIPsbel… 相似文献
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Interactions among Cu(Ⅱ),doxorubicin and copper operon C(CopC)have been investigated in detail by means of fluorescence,UV-Vis,IR spectra,isothermal titration calorimetry(ITC)and molecular docking in Tris-HCl buffer(50 mmol/L,pH=7.4,25℃).The results suggest that Cu(Ⅱ)-doxorubicin is formed in a Cu(Ⅱ)to doxorubicin molar ratio of 1:2,and the conditional stability constant,K[Cu(Ⅱ)-doxorubicin]is 1.90×10^9 L^2/mol^2,CopC and doxorubicin can form a 1:1 complex,the conditional stability constant is greater than 10^5 L/mol.Binding of doxorabicin causes a conformational change in CopC with the reduction of β-sheet and increase of random coil,and the stability of CopC is decreased.Cu(Ⅱ),doxorubicin and CopC can form a CopC-Cu(Ⅱ)-doxorubicin ternary complex.The formation of CopC-Cu(Ⅱ)-doxorubicin reduced greatly the reduction rate of Cu(Ⅱ)by ascorbate(Vc),i.e.,the binding of doxorubicin affects the action of CopC as redox switch. 相似文献
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以三维刚性结构的三蝶烯为单体, 通过简单的Friedel-Crafts烷基化反应制备得到高比表面积的三蝶烯基多孔有机聚合物(TPOP), 在TPOP中接枝乙二胺和氯乙酸钠, 构建了广谱重金属离子吸附剂(TPOP-CH2EDTA). 获得的TPOP-CH2EDTA具有微孔/介孔结构, 其微孔尺寸为1.6 nm, BET比表面积为634 m2/g, 利于重金属离子传递和配位作用的强化. TPOP-CH2EDTA对重金属离子具有吸附广谱性, 其对Ag(Ⅰ), Cu(Ⅱ), Ni(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Sn(Ⅳ), Pb(Ⅱ), Cd(Ⅱ), Fe(Ⅲ)和Cr(Ⅲ)等10种重金属离子的去除率均高于98%. 以Pb(Ⅱ)为典型的重金属污染物, 通过Langmuir模型计算得到Pb(Ⅱ)的最大吸附容量高达184.5 mg/g; 具有拟二级吸附动力学特征, 吸附速率快, 动力学常数k2为0.0173 g·mg?1·min?1; 经过5次循环使用后, Pb(Ⅱ)的去除效率仍高达95.8%. TPOP-CH2EDTA对混合溶液中Pb(Ⅱ)和Cu(Ⅱ)的去除率均高于99%, 且对含有大量无机盐[如Ca(Ⅱ), Mg(Ⅱ), K(Ⅰ)和Na(Ⅰ)离子]和有机化合物的复杂真实水体系, Pb(Ⅱ)和Cu(Ⅱ)的去除效率仍高于90%. 因此, 通过调控多孔有机聚合物微观结构(如比表面积、 孔径和吸附位点密度)而构筑的广谱性重金属吸附材料, 为协同去除复杂水系统中混合重金属离子提供了方案. 相似文献
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