Probing the mechanisms of macromolecular recognition: The cytochrome b ₅-cytochrome c complex

The specificity of complex formation between cytochrome b₅ (cyt b₅) and cytochrome c (cyt c) is believed to involve the formation of salt linkages between specific carboxylic acid residues of cyt b₅ with lysine residues on cyt c. Site-directed mutagenesis was used to alter the specified acidic residues of cyt b₅ to the corresponding amide analogues, which resulted in a lower affinity for complex formation with cyt c. The dissociation of the complex under high pressure resulted in specific volume changes, the magnitude of which reflected the degree of solvation of the acidic residues in the proposed protein-protein interface.