Unfolding process

The positive sign of AG° means that the unfolding process is unfavorable that is, the stable form of the protein at 54.5°C is the folded form. On the other hand, the relatively small magnitude of AG° means that the folded form is only slightly favored. Figure 3.4 shows the dependence of AG° on temperature for... 

Time-resolved IR spectra of similar peptides following a laser-excited temperature jump showed two relaxation times, unfolding 160 ns and faster components <10 ns (Williams et al., 1996). These times are very sensitive to the length, sequence, and environment of these peptides, but do show that the fundamental helix unfolding process is quite fast. These fast IR data have been contrasted with Raman and fluorescence-based T-jump experiments (Thompson et al., 1997). Raman experiments at various temperatures have suggested a folding in 1 /xs, based on an equilibrium analysis (Lednev et al., 2001). But all agree that the mechanism of helix formation is very fast. 

To get site-specific information about this unfolding process, a similar series of peptides, Ac-(AAAAK)3AAAA-YNH2, was sequentially labeled with 13C on the C=0 of four Ala residues, first on those at the N terminus, and then sequentially for the three other tetra-Ala positions (Decatur and Antonie, 1999). IR results showed a band shifted down 40 cm-1 from the amide F, which formed a clearly resolved band... 

Inui, T., et al. (2003). Characterization of the unfolding process of lipocalin-type prostaglandin D synthase. J. Biol. Chem. 278, 2845-52. 

The characteristics that discourage the use of RPLC for preparative isolation of bioactive proteins favor its use as an analytical tool for studying protein conformation. Chromatographic profiles can provide information on conformational stability of a protein and the kinetics of folding and unfolding processes. Information about solvent exposure of certain amino acid residues (e.g., tryptophan) as a function of the folding state can be obtained by on-line spectral analysis using diode array UV-vis detection or fluorescence detection. 

Similar approaches were also reported for chemically induced unfolding and a pH-induced one (73,74). Recently, Righetti reviewed the protein unfolding processes measured by CE and other techniques (75). 

In his discussion of The Abstractions of Space, Pawlowski additionally discloses that he, just like the Alchemists, had conceived of the world as essentially representing a dynamic, continuous, and unfolding process of successive trammutations ... 

Fig. 16 Thermal isomerisation of the photoisomer 33pJoto and the photochemical back reaction. The pyridine ligand moves from an external position to an intra-ring location while the - (CH2)i8 - fragment undergoes a folding/unfolding process...

Figure 8. A DSC record (a thermogram) from a thermally induced transition of lysozyme in dilute aqueous solution. Tt = transition temperature ACp = change in heat capacity accompanying the unfolding process. The hatched area is proportional to the enthalpy of transition. Adapted from Privalov (1980).

Figure 4.17 displays -galactosidase activity in the presence of 7 mM of guanidine chloride as a function of time. Analysis of the decay curve yields two decay times equal to 2.9 and 14.5 min. These times reveal mainly that the denaturation process of a protein does not occur in one simple step. The structure and dynamics of the protein should play an important role in the accessibility of the guanidine chloride to the amino acids and so to the unfolding process. 

Figure 10-2 shows the typical forces encountered as a function of the stretching distances where applied force less than 20 pN trigger unfolding processes, Clausen-Schaumann et al.5... 

Fig. 4. Profile of a differential scanning calorimetry experiment done on a synthetic lysozyme. The heat capacity (kilocalories per degree per mole) of the unfolding process was monitored as a function of temperature on a Micro-Cal MC2 instrument. The transition midpoint of protein unfolding corresponds to the temperature at the peak of the curve, and the thermodynamic parameters A H and A Cp are evaluated by the procedure of Privalov.33...

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