Interactions of cytochrome c and cytochrome f with aspartic acid peptides

Cytochrome c (cyt c) and cytochrome f (cyt f) molecular recognition charact ers and their structural changes due to complex formation with negatively c harged 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 th e same as those observed when cyt c interacted with plastocyanin (PC), indi cating that Aspptd's interacted with cyt c in the same way as PC. Conformat ional changes of cyt c due to interaction with Aspptd's observed by resonan ce Raman spectroscopy were similar to those reported for cyt c when bound w ith its native partner, cytochrome c oxidase. Electrochemical measurements showed that the redox potential of cyt c and cyt f shifted to lower potenti als 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 t he length and concentration of Aspptd. The observed structural and redox ch anges 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 pen ta-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 formati on.