Effects of charged peptides on electron transfer from [Fe(CN)(6)](4-) to cytochrome c or plastocyanin

Interactions of charged peptides, such as aspartic acid peptides (Aspptds) and lysine peptides (Lysptds), with cytochrome c (cyt c) or plastocyanin (P C) have been studied by measuring electron transfer between [Fe(CN)(6)](4-) and cyt c or PC in the presence of these peptides. Aspptds, up to penta-as partic acid, served as competitive inhibitors of electron transfer from [Fe (CN)(6)](4-) to oxidized cyt c, while Lysptds, up to penta-lysine, promoted electron transfer from [Fe(CN)(6)](4-) to oxidized PC. The electron transf er inhibitory effects of Aspptds are explained as competitive inhibition du e to neutralization of the positively charged amino acid residues at the su rface of cyt c by electrostatic interactions, whereas the electron transfer promoting effects of Lysptds may be due to formation of PC.Lysptd or Lyspt d.[Fe(CN)(6)](4-) complexes subsequently forming an electron transferring c omplex, PC.Lysptd.[Fe(CN)(6)](4-), without repulsion of the negative charge s. The inhibitory effect of Aspptds and promotional effect of Lysptds becam e significant as the net charge or concentration of the peptides increased. The promotional effects of Lysptds decreased as the net charge of the PC n egative patch was decreased by mutagenesis. Thus, charged peptides may serv e as a probe for investigation of the molecular recognition character of pr oteins.