Tigran V. Chalikian

Hydration and partial compressibility of biological compounds

We review the results of compressibility studies on proteins, nucleic acids, and systematically altered low molecular weight compounds that model the constituents of these biopolymers. The model compound data allow one to define the compressibility properties of water surrounding charged, polar, and nonpolar groups. These results, in conjunction with compressibility data on proteins and nucleic acids, were used to define the properties of water that is perturbed by the presence of these biopolymers in aqueous solutions. Throughout this review, we emphasize the importance of compressibility data for characterizing the hydration properties of solutes (particularly, proteins, nucleic acids, and their constituents), while describing how such data can be interpreted to gain insight into role that hydration can play in modulating the stability of and recognition between biologically important compounds.

Spectroscopic and volumetric investigation of cytochrome c unfolding at alkaline pH: characterization of the base-induced unfolded state at 25 degrees C.

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 cm3 g−1 and a compressibility decrease of 3.8 × 10−6 cm3 g−1 bar−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)