Hopping in the electron-transfer photocycle of the 1:1 complex of Zn-cytochrome c peroxidase with cytochrome c

Jennifer L. Seifert, Thomas D. Pfister, Judith M. Nocek, Yi Lu, Brian M. Hoffman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The physiological electron-transfer (ET) partners, cytochrome c peroxidase (CcP) and cytochrome c (Cc)1, can be modified to exhibit photoinitiated ET through substitution of Zn (or Mg) for Fe in either partner. Laser excitation of the Zn-porphyrin (ZnP) to its triplet excited state (3ZnP) initiates direct heme-heme ET to the ferriheme center of its partner across the protein-protein interface. This photoinitiated ET produces the charge-separated intermediate, I = [ZnP+CcP, Fe2+Cc], with a metalloporphyrin π-cation radical (ZnP+) in the donor protein and a ferroheme acceptor protein. I, in general, is thought to return to the ground state by a thermal ET process that involves direct heme-heme back-ET to complete a simple photocycle. We here contrast intracomplex ET between yeast iso-1 Cc and ZnCcP(WT) (wild-type) with that for two ZnCcP(X) variants: X = W191F, with redox-active W191 replaced by Phe; WYM4, a W191F mutant with further replacement of four other potentially redox-active sites (W51F, Y187F, Y229F, and Y236F). The results show that W191 acts as an ET mediator, which "short-circuits" the direct heme-heme back-ET through a two-step, hopping process in which the ZnP+ cation radical formed by photoinitiated ET rapidly oxidizes W191, and the resultant W191+, in turn, rapidly oxidizes Fe2+Cc.

Original languageEnglish (US)
Pages (from-to)5750-5751
Number of pages2
JournalJournal of the American Chemical Society
Volume127
Issue number16
DOIs
StatePublished - Apr 27 2005

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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