Acid Denaturation and Refolding of Cytochrome c on Silica Surface.

Denaturation of oxidized cytochrome c (cyt c) adsorbed to a hydrophilic fused silica surface was studied by UV-VIS attenuated total reflection (ATR) spectroscopy using a multiple optical pass system newly developed by this lab. Cyt c surface adsorption at neutral pH gave an adsorption equilibrium constant of Ka = 2 × 105 M−1 and a surface coverage at 63% of a monolayer saturation. Protein unfolding by acid denaturation was studied by equilibrating surface bound cyt c with acid buffers ranging in pH from 5 to 2. Protein orientation and surface coverage were calculated based on a theoretical model developed in previous work. The average heme tilt angle (44°) was found to be independent of pH, implicating protein-surface interactions as the dominant factor governing adsorption. A non-random molecular orientation distribution of cyt c on the surface was observed, providing further support for the dominance of protein-surface interactions. It was shown that when denaturing acid buffers were removed and replaced with a neutral buffer cyt c refolded, assuming their original conformation. The combination of unique, yet applicable, science and laboratory skills involved in this project had a tremendous impact on the authors' undergraduate curriculum, making it ideal for capstone project development. [ABSTRACT FROM AUTHOR]