title: Electron transfer among the CuA-, heme b- and a3-centers of Thermus thermophilus cytochrome ba3.
abstract: The 1-methyl-nicotinamide radical (MNA(*)), produced by pulse radiolysis has previously been shown to reduce the Cu(A)-site of cytochromes aa(3), a process followed by intramolecular electron transfer (ET) to the heme a but not to the heme a(3) [Farver, O., Grell, E., Ludwig, B., Michel, H. and Pecht, I. (2006) Rates and equilibrium of CuA to heme a electron transfer in Paracoccus denitrificans cytochrome c oxidase. Biophys. J. 90, 2131-2137]. Investigating this process in the cytochrome ba(3) of Thermus thermophilus (Tt), we now show that MNA(*) also reduces Cu(A) with a subsequent ET to the heme b and then to heme a(3), with first-order rate constants 11200 s(-1), and 770 s(-1), respectively. The results provide clear evidence for ET among the three spectroscopically distinguishable centers and indicate that the binuclear a(3)-Cu(B) center can be reduced in molecules containing a single reduction equivalent.
authors.affiliation: Institute of Analytical Chemistry, The Danish University of Pharmaceutical Sciences, Copenhagen, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Farver
authors.forename: Ying
authors.initials: Y
authors.lastname: Chen
authors.forename: James A
authors.initials: JA
authors.lastname: Fee
authors.forename: Israel
authors.initials: I
authors.lastname: Pecht
mesh_terms: D003573:Cytochrome b Group / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D007700:Kinetics; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D003573:Cytochrome b Group; D006418:Heme; C058557:cytochrome ba3; D003576:Electron Transport Complex IV