Correlation between the Stability and Redox Potential of Three Homologous Cytochromes c from Two Thermophiles and One Mesophile

摘要

The stability of the oxidized and reduced forms of three homologous cytochromes c from two thermophiles and one mesophile was systematically monitored by means of Soret absorption measurements in the presence of various concentrations of a denaturant, guani-dine thiocyanate, at pH 7.0 at 25 °C. Thermophilic Hydrogenobacter thermophilus cytochrome C_(552) was the most stable in both redox states, followed by moderately thermophilic Hydrogenophilus thermoluteolus cytochrome C_(552), and then mesophilic Pseudomonas aeruginosa cytochrome C_(551). Further stability and electrochemical analysis of the three proteins and the reciprocal variants, which exhibited a different hydrophobic interaction with the heme, showed that the one with the higher stability in both redox states had the lower redox potential. Consequently, these cytochromes c probably adapted to the cellular environments of the original bacteria with correlated stability and redox potential constraints, which are in part regulated by the hydrophobicity around the heme.