| Abstrakt: |
We have measured at 25°C the relative specific sound velocity increment, [u], and the partial specific volume, v°, of cytochrome c as a function of pH. Our data reveal that the base‐induced native to unfolded transition of the protein is accompanied by a volume decrease of 0.014 cm3g−1and a compressibility decrease of 3.8 × 10−6cm3g−1bar−1. These results allow us to conclude that, relative to a fully unfolded conformation, the base‐denatured state of cytochrome c has only 70 to 80% of its surface area exposed to the solvent. Recently, we reported a similar result for the acid‐denatured state of cytochrome c. Thus, insofar as solvent exposure is concerned, both the base‐ and the acid‐induced unfolded states of cytochrome c retain some order, with 20 to 30% of their surface areas remaining solvent‐inaccessible. We discuss the implications of this result in terms of defining potential intermediate states in protein folding pathways.—Chalikian, T. V., Gin‐ dikin, V. S., Breslauer, K. J. Spectroscopic and volumetric investigation of cytochrome c unfolding at alkaline pH: characterization of the base‐induced unfolded state at 25°C. FASEB J.10, 164‐170 (1996) |
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