Interactions of Cytochrome c and Cytochrome f with Aspartic Acid Peptides

Cytochrome c (cyt c ) and cytochrome f (cyt f ) molecular recognition characters and their structural changes due to complex formation with negatively charged aspartic acid peptides (Aspptd's) have been studied. Changes in the absorption spectrum of cyt c in the Soret region were detected when Aspptd's, up to penta -Asp, were added to the cyt c solution. These changes were the same as those observed when cyt c interacted with plastocyanin (PC), indicating that Aspptd's interacted with cyt c in the same way as PC. Conformational changes of cyt c due to interaction with Aspptd's observed by resonance Raman spectroscopy were similar to those reported for cyt c when bound with its native partner, cytochrome c oxidase. Electrochemical measurements showed that the redox potential of cyt c and cyt f shifted to lower potentials by 7−20 mV upon Aspptd binding, showing the enhancement in the electron donor ability of both cyt c and cyt f upon complex formation with Aspptd. The changes in the absorption spectrum and redox potential increased with the length and concentration of Aspptd. The observed structural and redox changes of cyt c and cyt f are attributed to adduct formations with Aspptd's by electrostatic interactions and suggest that similar changes would occur for cyt c and cyt f when interacting with proteins. Aspptd's, tetra - and penta -aspartic acid, served as competitive inhibitors of the electron transfer from cyt c or cyt f to PC, which was ascribable to the same adduct formation.