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The effect of three amino acids,histidine,phenylalanine and aspartic acid,as three different osmolytes,on the structure and activity of bovine carbonic anhydrase has been studied using different techniques.All the three amino acid...
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The effect of three amino acids,histidine,phenylalanine and aspartic acid,as three different osmolytes,on the structure and activity of bovine carbonic anhydrase has been studied using different techniques.All the three amino acids were found to stabilize the enzyme against inactivation alongside of time.While the thermal transition temperature was the same as control in all cases,DELTAG_(25) deg,a quantitative marker for thermal stability was found to be affected differently by the three amino acids.Besides,it seems that in the presence of phenylalanine,as a hydrophobic osmolyte,the structure of the enzyme is somehow exposed while aspartic acid,as a negatively charged amino acid,may induce the contraction of the protein.Histidine can make carbonic anhydrase get some extra secondary structure while the tertiary structure is not considerably changed.The in-vitro studies may make some points of view for future ex-vivo study on the effect of these osmolytes on the stability and activity of carbonic anhydrase.
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The effect of thiophenol on the kinetic of coumaric acid hydroxyla-tion by mushroom tyrosinase has been investigated at 20°C in 10 mM phosphate buffer solution,pH 5.3.The results show that thiophenol can activate or inhibit the c...
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The effect of thiophenol on the kinetic of coumaric acid hydroxyla-tion by mushroom tyrosinase has been investigated at 20°C in 10 mM phosphate buffer solution,pH 5.3.The results show that thiophenol can activate or inhibit the cresolase activity of mushroom tyrosinase depending to the concentration of thiophenol.It was proposed that the enzyme has two distinct sites for thiophenol.The first one is a high-affinity activation site and the other is a low-affinity inhibition site.Activation of the enzyme in the low concentration of thiophenol arises from increasing the affinity of binding for the substrate as well as increasing the enzyme catalytic constant.The resulting fluorescence spectra at low concentrations of the ligand clearly demonstrate typical enhancement of aromatic emission in the presence of thiophenol referring to the more exposed residues after the addition of thiophenol.Although the tertiary structure of the enzyme changes due to the activation of mushroom tyrosinase by binding of thiophenol,but it is not accompanied by a change in the secondary structure of mushroom tyrosinase.
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The molten globule state has been proposed as a major intermediate of protein folding. However it has proven difficult to obtain thermodynamic data characterizing this state. To explore an alternative approach for characterization...
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The molten globule state has been proposed as a major intermediate of protein folding. However it has proven difficult to obtain thermodynamic data characterizing this state. To explore an alternative approach for characterization of the molten globule state, n-alkyl sulfates induced formation of the molten globulte state of horse cytochrome c at pH 2 was studied by isothermal titration calorimetry (ITC). Titration of the acid unfolded state of cytochrome c with sodium octyl sulfate, sodium dodecyl sulfate or sodium tetradecyl sulfate, generated an exothermic reaction for formation of the molten globule state. The effects of various n-alkyl sulfates on the acid unfolded state of cytochrome c demonstrated that the increased alkyl chain length enhanced the exothermic values of calorimetric enthalpy and induced a more compact molten globule states. The heat contents agreed well with the conformational transition measured by molar ellipticity at 222 nm ([thetha]_(222))and Stoke radius (Rs) values. These results emphasize that isothermal titration calorimetry provides a reasonable alternative method for characterization of the molten globule state.
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The effect of sucrose as a very potent osmolyte and stabilizer on the structure and activity of bovine carbonic anhydrase has been studied using different techniques.Sucrose has been shown to stabilize the enzyme against inactivat...
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The effect of sucrose as a very potent osmolyte and stabilizer on the structure and activity of bovine carbonic anhydrase has been studied using different techniques.Sucrose has been shown to stabilize the enzyme against inactivation alongside of time.Besides,it seems that the enzyme got greater thermal stability in the existence of sucrose because both the transition temperature (T_m) and the standard Gibbs free energy (DELTAG_(25)) in protein thermal denaturation were increased.It seems that sucrose can have these effects through inducing some alterations in the structure of carbonic anhydrase.
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The interaction between whey carrier protein beta-lactoglobulin type A and B (BLG-A and -B) and 2,2'-bipyridin n-hexyl dithiocarbamato Pd(II) nitrate (BPHDC-Pd(II)),a new heavy metal complex designed for anticancer property,was in...
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The interaction between whey carrier protein beta-lactoglobulin type A and B (BLG-A and -B) and 2,2'-bipyridin n-hexyl dithiocarbamato Pd(II) nitrate (BPHDC-Pd(II)),a new heavy metal complex designed for anticancer property,was investigated by fluorescence spectroscopy combined with chemometry and circular dichroism (CD) techniques.A strong fluorescence quenching reaction of BPHDC-Pd(II) to BLG-A and -B was observed.Hence,BPHDC-Pd(II) complex can be bound to both BLG-A and -B,and quench the fluorescence spectra of the proteins.The quenching constant was determined using the modified Stern-Volmer equation.The binding parameters were evaluated by fluorescence quenching method.The results of binding study provided evidences presence of two and three sets of binding sites on the BLG-B and -A,respectively,for BPHDC-Pd(II) complex.Using fluorescence spectroscopy and chemometry,the ability of BLG-A and -B to form an intermediate upon interaction with BPHDC-Pd(II) complex was assessed.CD studies displayed that under influence of different concentrations of BPHDC-Pd(II) complex,the regular secondary structure of BLG-B had no significant changes,whereas for BLG-A a transition from alpha-helix to beta-structure was appeared.The results for both of BLG-A and -B displayed that BPHDC-Pd(lT) complex can induce a conformational transition from the native form to an intermediate state with a slightly opened conformation,which is detectable with chemometry analyses.
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Mushroom tyrosinase (MT)structural changes in the presence of Cu~(2+)and Ni~(2+)were studied separately.Far-UV CD spectra of the incubated MT with the either of the metal ions indicated reduction of the well-ordered secondary stru...
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Mushroom tyrosinase (MT)structural changes in the presence of Cu~(2+)and Ni~(2+)were studied separately.Far-UV CD spectra of the incubated MT with the either of the metal ions indicated reduction of the well-ordered secondary structure of the enzyme.Increasing in the maximum fluorescence emission of anilinonaphthalene-8-sulfonic acid (ANS)was also revealing partial unfolding caused by the conformational changes in the tertiary structure of MT.Thermodynamic studies on the chemical denaturation of MT by dodecyl trimethylammonium bromide (DTAB)showed decrease in the stability of MT in the presence of Cu~(2+)or Ni~(2+)using their activation concentrations.Both activities of MT were also assessed in the presence of different concentrations of these ions,separately,with various monophenols and their corresponding diphenols.Kinetic studies revealed that cresolase activity on p-coumaric acid was boosted in the presence of either of the metal ions,but inhibited when phenol,L-tyrosine,or 4-[(4-methylphenyl)azo]-phenol was substrate.Similarly,catecholase activity on caffeic acid was enhanced in the presence of Cu~(2+)or Ni~(2+),but inhibited when catechol,L-DOPA,or 4-[(4-methylbenzo)azo]-1,2-benzenediol was substrate.Results of this study suggest that both cations make MT more fragile and less active.However,the effect of the substrate structure on the MT allosteric behavior can not be ignored.
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Kinetic and thermodynamic studies were made on the binding of theobromine on the activity of adenosine deaminase (ADA) in 50 mM sodium phosphate buffer pH 7.5 at 300 K,using UV spec-trophotometry and isothermal titration calorimet...
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Kinetic and thermodynamic studies were made on the binding of theobromine on the activity of adenosine deaminase (ADA) in 50 mM sodium phosphate buffer pH 7.5 at 300 K,using UV spec-trophotometry and isothermal titration calorimetry (ITC).Theobromine acts as a competitive inhibitor.A graphical fitting method was used for determination of binding constant and enthalpy of inhibitor binding by using ITC data.The dissociation-binding constant is equal to 318 |iM by the calorimetry method,which agrees well with the value of 311 uM for the inhibition constant that was obtained from the spectroscopy method.The molar enthalpy and entropy of binding for theobromine are -15.80 kj/mol"1 and 14.30 J K"'mor',respectively.So,the binding process for theobromine on ADA is spontaneously by both enthalpy and entropy driven.
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A thermodynamic study on the interaction between magnesium and cobalt ions(M~(2+)),and human growth hormone,hGH,was studied at 27 °C in NaCl solution(50 mM)using the isothermal titration calorimetry.Isothermal titration calorimet...
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A thermodynamic study on the interaction between magnesium and cobalt ions(M~(2+)),and human growth hormone,hGH,was studied at 27 °C in NaCl solution(50 mM)using the isothermal titration calorimetry.Isothermal titration calorimetry was applied to obtain the binding isotherm for hGH+M~(2+).The results obtained indicate that there is a set of three identical and noninteracting binding sites for Cobalt ions and a set of two for magnesium.The extended solvation model was used to reproduce the enthalpies of M~(2+)+hGH interactions over the whole metal ions concentrations.The solvation parameters recovered from the solvation model were attributed to the structural change of hGH due to the metal ion interaction.The extended solvation model was applied to elucidate the effect of Mg~(2+)and Co~(2+)binding on the protein stability.
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The interaction of bovine carbonic anhydrase II with copper ions was studied by isothermal titration microcalorimetry,circular dichroism,UV spectrophotometry and temperature scanning spectrophotometry methods at 27degC in Tris buf...
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The interaction of bovine carbonic anhydrase II with copper ions was studied by isothermal titration microcalorimetry,circular dichroism,UV spectrophotometry and temperature scanning spectrophotometry methods at 27degC in Tris buffer solution at pH = 7.5.It was indicated that there are three non-identical different binding sites on carbonic anhydrase for Cu~(2+).The binding of copper ions is exothermic and can induce some minor changes in the secondary and tertiary structure of the enzyme,which does not unfold it,but can result in a decrease in both activity and stability of the enzyme.
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Heat of mixing is introduced as a guide for phase stability predictions of polymer mixtures, and an appropriate equation is presented for it. The fonn of this equation is a combined function of temperature and mixture composition....
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Heat of mixing is introduced as a guide for phase stability predictions of polymer mixtures, and an appropriate equation is presented for it. The fonn of this equation is a combined function of temperature and mixture composition. The capability of the presented equation has been treated qualitatively and it has been shown that all types of exothermic, endothermic, and s-shaped or sigmoidal heat of mixing CUIVes can be produced. Utilizing the low molecular weight analogue calorimetly method, heat of mixing was measured at two temperatures, 27°C and 37°C for three polymer mixtures-po1y(styrene)/poly(vinylchloride) (PS/PVC), poly(styrene)/ poly(methylmethacrylate) (PS/PMMA), and poly(styrene)/poly(vinylacetate) (PS/ PVAc) at an entire composition range. It has been shown that excellent agreement between the results of the calculations and the experimental heat of mixing data was achieved. Using the results of analogue calorimetric measurements for phase stability studies of polymer mixtures, it was found that often, acceptable predic- tions can be made by this method, but they are not always completely true.
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