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