Syed Ikramul Hasan, Faizan Ahmad
Protein research laboratory, Centre for interdisciplinary research in basic science Jamia Millia Islamia, New Delhi-1100025, India.
The properties of urea-induced unfolding transition of iso-1 cytochrome c (iso-1) from Saccharomyces cerevisiae have been investigated by equilibrium method and have been compared with previously published studies of horse cytochrome c, which differs from iso-1 by 40% in amino acid sequence. Measurements of absorbance and circular dichroism in the ultraviolet and visible spectral regions as a function of urea concentration shows that the unfolding of iso-1 cyt-c is not a two-state process, for (a) the normalized transition curves of two different optical probes do not coincide with one another, and (b) ∆G0° D (Gibbs free energy of denaturation in the absence of urea), Cm (midpoint of denaturation) and md (slope of the plot of ∆G° D verses urea concentration) values obtained from different optical probes do not match with one another. We have shown from the reversible unfolding transition of iso-1 cytochrome c from Saccharomyces cerevisiae that this protein is considerably less stable toward denaturation by urea than is the homologous cytochrome c from horse. The estimated differences in stability of the two proteins in the absence of denaturant are in reasonable agreement with theoretical expectations based on the numbers and types of buried hydrophobic groups. Read more…