A class of polyanionic copper porphyrin dimers is shown to selectively increase the susceptibilityof cytochrome c to proteolysis through binding-induced disruption of tertiary and secondary structure. Thefree energy of the protein conformation leading to proteolytic attack is stabilized by about 2.4 kcal/mol inthe bound state. The proteolytic acceleration is catalytic in nature, requiring only a fraction of an equivalentof metalloporphyrin to effect complete, rapid digestion in the presence of a protease.1