Circular dichroism unfolded

UNFOLDED PEPTIDES AND PROTEINS STUDIED WITH INFRARED ABSORPTION AND VIBRATIONAL CIRCULAR DICHROISM SPECTRA... 

Fig. 29. Equilbrium unfolding of C40A/C82A/P27A (pseudo-wild-type) barstar monitored by A R, mean residue circular dichroism. Conditions for near-UV CD were 50 /xM protein in 50 mM Tris-HCl buffer, pH 8, 0.1 M KC1, path length 1 cm. (A) Urea-induced unfolding at 25°C at urea concentrations as indicated. (B) Cold-induced unfolding in...

Fig. 4. Time-induced conformational change of spider silk protein (spidroin) in solution. Solutions of silk proteins at 1% w/v in distilled water were monitored using circular dichroism. The graph shows a change in secondary structure with time. The silk proteins underwent a kinetically driven transition from a partially unfolded structure to a -sheet-rich structure (from Dicko et al., 2004c). ( ) after 0 days, (O) after 1 day, and (A) after 2 days. The conformational change appeared faster at 20°C compared to 5°C, suggesting a hydrophobically driven mechanism. (Copyright 2004 American Chemical Society.)...

Fig. 5. The effect of protein-protein interactions on Nephila edulis major ampullate circular dichroism spectra in solution. A change in secondary structure with increasing concentration is observed. At low concentration (minimal protein-protein interactions) silk proteins appear partially unfolded in solution. At higher concentration (higher protein-protein interactions) silk proteins refold into a helix-like structure, most likely a molten-like globule (from Dicko et al., 2004c). This final molten structure would facilitate local chain rearrangement while preserving the global structure for protein storage and transport. (Copyright 2004 American Chemical Society.)...

Circular dichroism measurements on soluble Sup35pN and NM domains indicate a largely unfolded structure (Glover et al, 1997 King et al., 1997). 

Zaiss, K. and R. Jaenicke. 1999. Thermodynamic study of phosphoglycerate kinase from Thermotoga maritima and its isolated domains reversible thermal unfolding monitored by differential scanning calorimetry and circular dichroism spectroscopy. Biochemistry 38 4633 -639. 

If the incoming light is polarised, any chiral features of the molecule that absorbs will be highlighted—in particular changes in such chiral features, e.g. when the protein is unfolding, these features will stand out. The secondary stmctural elements of proteins are chiral in their nature. This phenomenon can be followed with the so-called circular dichroism (CD). ... 

Figure 17.1 Thermal unfolding of bamase measured by calorimetry and spectroscopy. The heat capacity of bamase (trace A) was measured using differential scanning calorimetry with a baseline (trace B) of buffer versus buffer Tm is 310.9 0.01 K, A D-N(cai) = 98.4 0.2kcal/mol, and A//D N(vh) = 98.1 0.3 kcal/mol. The ellipticity at 230 nm in the circular dichroism (trace C) under identical conditions fits Tm = 310.5 0.1 K, and A//D N(vh) = 93 3 kcal/mol (equation 17.5).

The fraction unfolded, [D]/([D] + [N]), may be determined by spectroscopy (for example, absorbance, fluorescence, or circular dichroism) and fitted to equation 17.5. The enthalpy term derived from these experiments is referred to as the van t Hoff value, AHD N(vh). (Note that the specific heat terms of equations 17.1 and 17.2 have to be substituted into the equation.)... 

Alanine racemase of B. stearothermophilus consists of two identical subunits, whereas both DadB and air enzymes of Salmonella typhimurium and the Streptococcusfaecalis enzyme occur in a form of monomer. Toyama et al.14) examined whether the monomeric form of the B. stearothermophilus enzyme is catalytically active. They studied the guanidine HC1-induced subunit dissociation and unfolding of the enzyme by fluorescence and absorption spectroscopies, circular dichroism (CD) analysis, and gel filtration.I4) The overall process was found to be reversible more than 75% of the original activity was recovered by decreasing the denaturant concentration. 

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