We have used zinc-substituted hemoproteins to study long-range electron transfer between redox centers at fixed and known distances. The photo-excited zinc triplet state in one subunit of the α1-β2 electron transfer complex of [Zn,Fe] hybrid hemoglobin transfers an electron to its partner aquoferriheme subunit at a rate, kt=100 s-1. The temperature dependence of this electron transfer from 77K to 313K is indicative of non-adiabatic electron tunnelling in which the accompanying nuclear rearrangements proceed by nuclear tunnelling. For the complex between zinc-substituted yeast cytochrome c peroxidase (CCP) and native yeast cytochrome c, electron transfer occurs at a rate, kt=138 s-1, compared to kt = 17 s-1 in the complex between the yeast enzyme and horse cyt c. The difference demonstrates the species specificity involved in physiological electron transfer. Oxidation of ferroporphyrin by the zinc porphyrin radical is more rapid, and, for the yeast cytochrome, occurs with a rate, kh ∼ 104 s-1.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry