Folding thermally induced

VJ Hilser, CD Worosila, E Freire. Analysis of thermal-induced proteins folding/ unfolding transitions using free-solution capillary electrophoresis. Anal. Biochem. 208 125-131 (1993). 

Figure 16.5 (a) The native folded state of the protein and the unfolded, denatured state following the thermally-induced structural change (b) the duplex state of nucleic acids, stable at low temperatures, in which the bases are paired and stacked, and the monomer states following the thermal disruption in which the bases are unpaired and randomly arranged along the backbone. 

The increased thermostability of the disulfide mutant is also shown by denaturation temperature estimated by differential scanning calorimetry (Fig. 12.4). Tm (midpoint temperature in the thermally induced transition from the folded to the unfolded state) of the mutant enzyme is 63.0°C, which is 4.5°C higher than that of the wild-type enzyme (58.5 °C). Under reducing conditions, the Tm of the mutant enzyme is decreased to 50.5 ° C, which is lower than that of the wild-type enzyme, indicating that the disulfide bond formation is required for the thermostability and that the mutant enzyme with free cysteine residues does not have a stable structure like the wild-type enzyme. 

In this section we discuss the change that occur in the melting of DNA and RNA. The term melting is used to refer a thermally induced transition of a double-helical nucleic acid from an ordered double helix to a disordered state. Native RNA is usually single stranded, but it folds back on itself to form double helical sequences. Raman spectroscopy does not appear to be sensitive to the tertiary structure of RNA, but it can tell what fraction of the RNA is in double-helical form. ... 

Percec and coworkers have shown that the oriented fibers of dendronized polyacetylenes can undergo thermally induced mechanical motion [38]. In this system (Figure 37.12), the dendrons around the polymer backbone become self-organized and thus facilitate a reversible ciscoid-to-transoid conformational isomerism of the polymer backbone. This isomerism is then converted into unidirectional macroscopic motion along the fiber axis. Remarkably, this mechanical motion could be used to displace objects with a mass of up to 250-fold that of the polymer fiber. 

Heat denaturation is a fairly simple process the thermal motimis shake apart the weakly bound protein folds. Pressure-induced denaturatimi seems, crudely speaking, to stem from the squeezing of solvent so that it enters and loosens the compact native state. And for cold denaturation, the cmiventional view has been that the hydrophobic groups get more soluble in water (that is, the hydrophobic interaction... 

Thermally stable nitrilase from Streptomyces sp. MTCC 7546 was induced by benzonitrile enrichment. While discovered by induction with aromatic nitrile, the enzyme was shown to exhibit a strong preference for aliphatic nitriles, with as high as 30-fold greater activity with aliphatic substrates compared with benzonitrile. The enzyme displays optimal activity at pH 7 and 50 °C [56]. 

In this case, a moderately water-soluble amphiphilic N-vinylcaprolaclam (NVC1) played the role of a fl-unit, and a well-water-compatible N-vinyl-imidazole (NVIAz) served as a P-unil. The polymerization was carried out in a medium of 10% aqueous dimethylsulfoxide (DMSO). The addition of DMSO to the reaction solvent was necessary because of insufficient NVC1 solubility in pure water. It was also shown that in this solvent mixture, the NVCl-homopolymers and NVCl/NVIAz-copolymers retained their LCST-behaviour [26,28]. Hence, the DMSO in the reaction solvent did not significantly suppress the hydrophobic interactions of the NVC1 units. The polymerization was initiated by the redox system (N,N,N, N -tetramethylethylenediamine (TMEDA) + ammonium persulphate (APS)) and was carried out at 65 °C (1st step). This condition was very important, since admittedly the temperature was higher than the phase separation threshold of the reaction bulk when the polymeric products were formed that is, under these thermal conditions, hydrophobically-induced folding as the NVCl-blocks appear was ensured. After completion of the reaction, the... 

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