DRAMATIC STABILIZATION OF FERRICYTOCHROME-C UPON REDUCTION

By combining measurements of the free energy of denaturation of the C1 02T variant of Saccharomyces cerevisiae iso-1-ferricytochrome c with d etermination of the formal potentials for the native and chemically-de natured states we have determined the free energy of denaturation of t he ferro form of the protein. We report that the simplest of all chemi cal modifications, addition of an electron, increases the stability of ferricytochrome c by approximately 10 kcal mol-1 at 300 K, pH 4.6. Th is makes reduced cytochrome c one of the most stable proteins yet inve stigated.