Measurements characterizing electron transfer from a photoexcited zinc protoporphyrin triplet (3ZnP) to a ferriheme electron acceptor within the [alpha 1,beta 2] electron-transfer complex of [FeIII,Zn] hybrid hemoglobins are reported. Analytical results demonstrate that the hybrids studied are pure, homogeneous proteins with 1:1 ZnP:FeP content. Within the T quaternary structure adopted by these hybrids, the optical spectrum of a FeIIIP is perturbed by the protein environment. Room temperature kinetic studies of the rate of 3ZnP decay as a function of the heme oxidation and ligation state demonstrate that quenching of 3ZnP by FeIII(H2O)P occurs by long-range intramolecular electron transfer with rate constant kt = 100 (+/- 10) s-1 and is not complicated by spin-quenching or energy-transfer processes; results are the same for alpha(Zn) and beta(Zn) hybrids. Replacement of H2O as a ligand to the ferriheme changes the 3ZnP----FeIIIP electron-transfer rate constant, kt, which demonstrates that electron transfer, not conformational conversion, is rate limiting. However, the trend is not readily explained by simple considerations of spin-state and bonding geometry: kt decreases in the order imidazole greater than H2O greater than F- approximately CN- approximately N3-. The reverse electron-transfer process FeIIP----ZnP+ has not been observed directly but has been shown to be much more rapid, with rate constant kb greater than 10(3) s-1, consistent with the possible importance of "hole" superexchange in electron tunneling within protein complexes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.