Study of interaction between DNA and intercalator at molecular level is important to understand the mechanisms of DNA replication and repair. A micro-fabricated local heating thermodevice was adapted to perform denaturation experiments of DNA with fluorescent intercalator on millisecond time scale. Response time of complete unzipping of double stranded DNA, 16 μm in length, was measured to be around 5 min by commercial thermocycler. Response time of quenching of double stranded DNA with fluorescent intercalator SYBR Green was measured to be 10 ms. Thus, quenching properties owing to strand unzipping and denaturation at base pair level were distinguished. This method has provided easy access to measure this parameter and may be a powerful methodology in analyzing biomolecules on millisecond time scale. 相似文献
The objective of this work is identifying changes in the collagen bands in heated and rehydrated dentine. We use bovine dentine slices that were heated in oven between 100 and 300 degrees C. The sample hydration was conducted in sodium chloride solution at 0.9 wt.%; the spectra were acquired by a Fourier transform infrared spectrometer in the spectral range of 4000-400 cm-1. Our results show a temperature range (T225 degrees C) where the collagen is denatured and no reversion is observed after rehydration. This work identifies an important characteristic that dentinal collagen can assume when the tissue is heated and rehydrated; these results indicate the denaturation temperature of dentinal collagen to be near 175-200 degrees C. 相似文献
The chemical denaturation of RNase A was found to be mediated by sodium dodecyl sulfate (SDS) at various pH. The characterization of the unfolding pathway was investigated by spectrophotometry and differential scanning calorimetry (DSC), and was analyzed by multivariate curve resolution (MCR) as a chemometric method. The spectrophotometric titration curve of RNase A upon interaction with SDS indicated a distinct complex intermediate in glycine buffer at pH 3.3. This was accompanied with the catalytic activation of the enzyme and was concurrent with maximum population of the intermediate, determined by MCR. This was confirmed by the DSC profile of RNase A in the presence of SDS, indicated by two transitions in thermal unfolding. The kinetic data on the unfolding process of RNase A upon addition of SDS showed a two-phase pathway under the same conditions. The intermediate appeared at low pH especially at the pKa of SDS (pH 3.3). These results provide strong evidence of the influence of low pH (around the pKa of SDS) on the existence of an intermediate upon interaction of RNase A with SDS. 相似文献
The effect of urea and n-propanol on circular dichroism (CD) and viscosity of purified type1 collagen solution at various temperatures and differential scanning calorimetry (DSC) of rat-tail tendon (RTT) collagen fibre have been studied. CD reveals a spectrum with a positive peak at around 220 nm and a negative peak at 200 nm characteristics of collagen triple helix. The molar ellipticity decreases as the concentration of urea increases up to particular concentration (collagen solution treated with 265 μM of urea) and after that it increases (collagen solution treated with 500 μM of urea). There is a linear decrease in molar ellipticity as the concentration of n-propanol increases. Denaturation temperature of urea and n-propanol treated with purified collagen solution has been studied using viscosity method. Additives such as urea and n-propanol decrease the thermal stability of collagen triple helix in solution and in RTT collagen fibre. Thermal helix to coil transition of urea and n-propanol treated collagen depends on the degree of hydration and the concentration of these additives. Thermodynamic parameters such as the peak temperature, enthalpy of activation, and energy of activation for collagen-gelatin transition for native, urea and n-propanol treated RTT collagen fibre has been calculated using DSC. The change in the thermodynamic parameters has been observed for native, urea and n-propanol treated RTT collagen fibres. The experimental results show that the change in the water structure, dehydration and desolvation induced by different additives such as urea and n-propanol on RTT may vary with the type of denaturation. 相似文献
The cations, in the form of salt, present in a solution containing DNA play a crucial role in the opening of the two strands of DNA. We use a simple non-linear model and investigate the role of these cations on the mechanical unzipping of DNA. The Hamiltonian is modified to incorporate the solvent effect and the presence of these cations in the solution. We calculate the melting temperature as well as the critical force that is required to unzip the DNA molecule as a function of salt concentration of the solution. The phase diagrams are found to be in close agreement with the experimental phase diagrams. 相似文献
Transitions in the tryptophan microenvironment and secondary structure of two monocot lectins from Sauromatum guttatum and Arisaema tortuosum under different denaturing conditions were studied by steady state and time resolved fluorescence and CD spectroscopy. The
lectins exist as tetramers with a single tryptophan residue estimated per monomer, present in a polar environment. Quenching
with ionic quenchers showed predominantly electropositive environment for tryptophan residues. Acrylamide had maximum quenching
effect. A decrease in KI quenching due to lectin denaturation indicated redistribution of charges as a result of possible
conformational change. The two values for lifetimes of tryptophanyl population (1.2–1.4 and 6.3–6.4 ns) reduced substantially
on quenching or denaturation. Similarly, both the lectins showed a drastic loss of secondary structure in 5 M Gdn-HCl or 6 M
Urea or at pH 2.0 and below. For the first time araceous lectins, like legume lectins are shown to bind adenine. The presence
of a compact structure at alkaline pH 10.0–12.0 was observed in CD spectra. 相似文献
In the present study, the heat-induced interaction between whey proteins and casein micelles was studied. To that end, the particle size distribution of 5.5% (w/w) casein micellar dispersions was determined by photon correlation spectroscopy as a function of both the whey protein concentration and heating time at 80 °C. The results clearly indicated that heat-induced aggregation of the casein micelles only occurred in the presence of whey proteins.
In an effort to overcome the heat-induced interactions between whey proteins and casein micelles, the influence of different soybean lecithins was investigated. Comparing native to hydrolysed, as well as hydroxylated soybean lecithin, it was observed that the heat-stabilising effect of the lecithins was directly related to their hydrophilicity: whereas native soybean lecithin had hardly any beneficial effect, highly hydrolysed as well as hydroxylated soybean lecithin largely prevented heat-induced casein micelle aggregation in the presence of whey proteins.
From experimental observations on the heat-induced decrease of whey protein solubility both in the absence and presence of hydrolysed lecithin, it was deduced that the latter may stabilise the exposed hydrophobic surface sites of heat-denatured whey proteins. Dynamic surface tension measurements indicated that the heat-stabilising properties of lecithins were mainly determined by their critical aggregation concentration. 相似文献